diff --git a/development/auto-changelog.js b/development/auto-changelog.js
index 8a6d8f08a..455bf5beb 100755
--- a/development/auto-changelog.js
+++ b/development/auto-changelog.js
@@ -1,25 +1,27 @@
 #!/usr/bin/env node
 const fs = require('fs').promises;
-const assert = require('assert').strict;
-const path = require('path');
-const { escapeRegExp } = require('lodash');
-const { version } = require('../app/manifest/_base.json');
-const runCommand = require('./lib/runCommand');
 
-const URL = 'https://github.com/MetaMask/metamask-extension';
+const path = require('path');
+const { version } = require('../app/manifest/_base.json');
+const { updateChangelog } = require('./lib/changelog/updateChangelog');
+const { unreleased } = require('./lib/changelog/constants');
+
+const REPO_URL = 'https://github.com/MetaMask/metamask-extension';
 
 const command = 'yarn update-changelog';
 
 const helpText = `Usage: ${command} [--rc] [-h|--help]
 Update CHANGELOG.md with any changes made since the most recent release.
+
 Options:
       --rc    Add new changes to the current release header, rather than to the
-                'Unreleased' section.
+                '${unreleased}' section.
   -h, --help  Display this help and exit.
 
-New commits will be added to the "Unreleased" section (or to the section for the
+New commits will be added to the "${unreleased}" section (or to the section for the
 current release if the '--rc' flag is used) in reverse chronological order. Any
 commits for PRs that are represented already in the changelog will be ignored.
+
 If the '--rc' flag is used and the section for the current release does not yet
 exist, it will be created.
 `;
@@ -42,158 +44,19 @@ async function main() {
     }
   }
 
-  await runCommand('git', ['fetch', '--tags']);
-
-  const [mostRecentTagCommitHash] = await runCommand('git', [
-    'rev-list',
-    '--tags',
-    '--max-count=1',
-  ]);
-  const [mostRecentTag] = await runCommand('git', [
-    'describe',
-    '--tags',
-    mostRecentTagCommitHash,
-  ]);
-  assert.equal(mostRecentTag[0], 'v', 'Most recent tag should start with v');
-
-  const commitsSinceLastRelease = await runCommand('git', [
-    'rev-list',
-    `${mostRecentTag}..HEAD`,
-  ]);
-
-  const commitEntries = [];
-  for (const commit of commitsSinceLastRelease) {
-    const [subject] = await runCommand('git', [
-      'show',
-      '-s',
-      '--format=%s',
-      commit,
-    ]);
-
-    let prNumber;
-    let description = subject;
-
-    // Squash & Merge: the commit subject is parsed as `<description> (#<PR ID>)`
-    if (subject.match(/\(#\d+\)/u)) {
-      const matchResults = subject.match(/\(#(\d+)\)/u);
-      prNumber = matchResults[1];
-      description = subject.match(/^(.+)\s\(#\d+\)/u)[1];
-      // Merge: the PR ID is parsed from the git subject (which is of the form `Merge pull request
-      // #<PR ID> from <branch>`, and the description is assumed to be the first line of the body.
-      // If no body is found, the description is set to the commit subject
-    } else if (subject.match(/#\d+\sfrom/u)) {
-      const matchResults = subject.match(/#(\d+)\sfrom/u);
-      prNumber = matchResults[1];
-      const [firstLineOfBody] = await runCommand('git', [
-        'show',
-        '-s',
-        '--format=%b',
-        commit,
-      ]);
-      description = firstLineOfBody || subject;
-    }
-    // Otherwise:
-    // Normal commits: The commit subject is the description, and the PR ID is omitted.
-
-    commitEntries.push({ prNumber, description });
-  }
-
   const changelogFilename = path.resolve(__dirname, '..', 'CHANGELOG.md');
-  const changelog = await fs.readFile(changelogFilename, { encoding: 'utf8' });
-  const changelogLines = changelog.split('\n');
+  const changelogContent = await fs.readFile(changelogFilename, {
+    encoding: 'utf8',
+  });
 
-  const prNumbersWithChangelogEntries = [];
-  for (const line of changelogLines) {
-    const matchResults = line.match(/- \[#(\d+)\]/u);
-    if (matchResults === null) {
-      continue;
-    }
-    const prNumber = matchResults[1];
-    prNumbersWithChangelogEntries.push(prNumber);
-  }
+  const newChangelogContent = await updateChangelog({
+    changelogContent,
+    currentVersion: version,
+    repoUrl: REPO_URL,
+    isReleaseCandidate,
+  });
 
-  const changelogEntries = [];
-  for (const { prNumber, description } of commitEntries) {
-    if (prNumbersWithChangelogEntries.includes(prNumber)) {
-      continue;
-    }
-
-    let changelogEntry;
-    if (prNumber) {
-      const prefix = `[#${prNumber}](${URL}/pull/${prNumber})`;
-      changelogEntry = `- ${prefix}: ${description}`;
-    } else {
-      changelogEntry = `- ${description}`;
-    }
-    changelogEntries.push(changelogEntry);
-  }
-
-  if (changelogEntries.length === 0) {
-    console.log('CHANGELOG required no updates');
-    return;
-  }
-
-  const versionHeader = `## [${version}]`;
-  const escapedVersionHeader = escapeRegExp(versionHeader);
-  const currentDevelopBranchHeader = '## [Unreleased]';
-  const currentReleaseHeaderPattern = isReleaseCandidate
-    ? // This ensures this doesn't match on a version with a suffix
-      // e.g. v9.0.0 should not match on the header v9.0.0-beta.0
-      `${escapedVersionHeader}$|${escapedVersionHeader}\\s`
-    : escapeRegExp(currentDevelopBranchHeader);
-
-  let releaseHeaderIndex = changelogLines.findIndex((line) =>
-    line.match(new RegExp(currentReleaseHeaderPattern, 'u')),
-  );
-  if (releaseHeaderIndex === -1) {
-    if (!isReleaseCandidate) {
-      throw new Error(
-        `Failed to find release header '${currentDevelopBranchHeader}'`,
-      );
-    }
-
-    // Add release header if not found
-    const firstReleaseHeaderIndex = changelogLines.findIndex((line) =>
-      line.match(/## \[\d+\.\d+\.\d+\]/u),
-    );
-    const [, previousVersion] = changelogLines[firstReleaseHeaderIndex].match(
-      /## \[(\d+\.\d+\.\d+)\]/u,
-    );
-    changelogLines.splice(firstReleaseHeaderIndex, 0, versionHeader, '');
-    releaseHeaderIndex = firstReleaseHeaderIndex;
-
-    // Update release link reference definitions
-    // A link reference definition is added for the new release, and the
-    // "Unreleased" header is updated to point at the range of commits merged
-    // after the most recent release.
-    const unreleasedLinkIndex = changelogLines.findIndex((line) =>
-      line.match(/\[Unreleased\]:/u),
-    );
-    changelogLines.splice(
-      unreleasedLinkIndex,
-      1,
-      `[Unreleased]: ${URL}/compare/v${version}...HEAD`,
-      `[${version}]: ${URL}/compare/v${previousVersion}...v${version}`,
-    );
-  }
-
-  // Ensure "Uncategorized" header is present
-  const uncategorizedHeaderIndex = releaseHeaderIndex + 1;
-  const uncategorizedHeader = '### Uncategorized';
-  if (changelogLines[uncategorizedHeaderIndex] !== '### Uncategorized') {
-    const hasEmptyLine = changelogLines[uncategorizedHeaderIndex] === '';
-    changelogLines.splice(
-      uncategorizedHeaderIndex,
-      0,
-      uncategorizedHeader,
-      // Ensure an empty line follows the new header
-      ...(hasEmptyLine ? [] : ['']),
-    );
-  }
-
-  changelogLines.splice(uncategorizedHeaderIndex + 1, 0, ...changelogEntries);
-  const updatedChangelog = changelogLines.join('\n');
-  await fs.writeFile(changelogFilename, updatedChangelog);
+  await fs.writeFile(changelogFilename, newChangelogContent);
 
   console.log('CHANGELOG updated');
 }
diff --git a/development/lib/changelog/changelog.js b/development/lib/changelog/changelog.js
new file mode 100644
index 000000000..07c0cd01c
--- /dev/null
+++ b/development/lib/changelog/changelog.js
@@ -0,0 +1,275 @@
+const semver = require('semver');
+
+const { orderedChangeCategories, unreleased } = require('./constants');
+
+const changelogTitle = '# Changelog';
+const changelogDescription = `All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).`;
+
+// Stringification helpers
+
+function stringifyCategory(category, changes) {
+  const categoryHeader = `### ${category}`;
+  if (changes.length === 0) {
+    return categoryHeader;
+  }
+  const changeDescriptions = changes
+    .map((description) => `- ${description}`)
+    .join('\n');
+  return `${categoryHeader}\n${changeDescriptions}`;
+}
+
+function stringifyRelease(version, categories, { date, status } = {}) {
+  const releaseHeader = `## [${version}]${date ? ` - ${date}` : ''}${
+    status ? ` [${status}]` : ''
+  }`;
+  const categorizedChanges = orderedChangeCategories
+    .filter((category) => categories[category])
+    .map((category) => {
+      const changes = categories[category];
+      return stringifyCategory(category, changes);
+    })
+    .join('\n\n');
+  if (categorizedChanges === '') {
+    return releaseHeader;
+  }
+  return `${releaseHeader}\n${categorizedChanges}`;
+}
+
+function stringifyReleases(releases, changes) {
+  const stringifiedUnreleased = stringifyRelease(
+    unreleased,
+    changes[unreleased],
+  );
+  const stringifiedReleases = releases.map(({ version, date, status }) => {
+    const categories = changes[version];
+    return stringifyRelease(version, categories, { date, status });
+  });
+
+  return [stringifiedUnreleased, ...stringifiedReleases].join('\n\n');
+}
+
+function withTrailingSlash(url) {
+  return url.endsWith('/') ? url : `${url}/`;
+}
+
+function getCompareUrl(repoUrl, firstRef, secondRef) {
+  return `${withTrailingSlash(repoUrl)}compare/${firstRef}...${secondRef}`;
+}
+
+function getTagUrl(repoUrl, tag) {
+  return `${withTrailingSlash(repoUrl)}releases/tag/${tag}`;
+}
+
+function stringifyLinkReferenceDefinitions(repoUrl, releases) {
+  const orderedReleases = releases
+    .map(({ version }) => version)
+    .sort((a, b) => semver.gt(a, b));
+
+  // The "Unreleased" section represents all changes made since the *highest*
+  // release, not the most recent release. This is to accomodate patch releases
+  // of older versions that don't represent the latest set of changes.
+  //
+  // For example, if a library has a v2.0.0 but the v1.0.0 release needed a
+  // security update, the v1.0.1 release would then be the most recent, but the
+  // range of unreleased changes would remain `v2.0.0...HEAD`.
+  const unreleasedLinkReferenceDefinition = `[${unreleased}]: ${getCompareUrl(
+    repoUrl,
+    `v${orderedReleases[0]}`,
+    'HEAD',
+  )}`;
+
+  // The "previous" release that should be used for comparison is not always
+  // the most recent release chronologically. The _highest_ version that is
+  // lower than the current release is used as the previous release, so that
+  // patch releases on older releases can be accomodated.
+  const releaseLinkReferenceDefinitions = releases
+    .map(({ version }) => {
+      if (version === orderedReleases[orderedReleases.length - 1]) {
+        return `[${version}]: ${getTagUrl(repoUrl, `v${version}`)}`;
+      }
+      const versionIndex = orderedReleases.indexOf(version);
+      const previousVersion = orderedReleases
+        .slice(versionIndex)
+        .find((releaseVersion) => {
+          return semver.gt(version, releaseVersion);
+        });
+      return `[${version}]: ${getCompareUrl(
+        repoUrl,
+        `v${previousVersion}`,
+        `v${version}`,
+      )}`;
+    })
+    .join('\n');
+  return `${unreleasedLinkReferenceDefinition}\n${releaseLinkReferenceDefinitions}${
+    releases.length > 0 ? '\n' : ''
+  }`;
+}
+
+/**
+ * @typedef {import('./constants.js').Unreleased} Unreleased
+ * @typedef {import('./constants.js').ChangeCategories ChangeCategories}
+ */
+/**
+ * @typedef {import('./constants.js').Version} Version
+ */
+/**
+ * Release metadata.
+ * @typedef {Object} ReleaseMetadata
+ * @property {string} date - An ISO-8601 formatted date, representing the
+ *   release date.
+ * @property {string} status -The status of the release (e.g. 'WITHDRAWN', 'DEPRECATED')
+ * @property {Version} version - The version of the current release.
+ */
+
+/**
+ * Category changes. A list of changes in a single category.
+ * @typedef {Array<string>} CategoryChanges
+ */
+
+/**
+ * Release changes, organized by category
+ * @typedef {Record<keyof ChangeCategories, CategoryChanges>} ReleaseChanges
+ */
+
+/**
+ * Changelog changes, organized by release and by category.
+ * @typedef {Record<Version|Unreleased, ReleaseChanges>} ChangelogChanges
+ */
+
+/**
+ * A changelog that complies with the ["keep a changelog" v1.1.0 guidelines]{@link https://keepachangelog.com/en/1.0.0/}.
+ *
+ * This changelog starts out completely empty, and allows new releases and
+ * changes to be added such that the changelog remains compliant at all times.
+ * This can be used to help validate the contents of a changelog, normalize
+ * formatting, update a changelog, or build one from scratch.
+ */
+class Changelog {
+  /**
+   * Construct an empty changelog
+   *
+   * @param {Object} options
+   * @param {string} options.repoUrl - The GitHub repository URL for the current project
+   */
+  constructor({ repoUrl }) {
+    this._releases = [];
+    this._changes = { [unreleased]: {} };
+    this._repoUrl = repoUrl;
+  }
+
+  /**
+   * Add a release to the changelog
+   *
+   * @param {Object} options
+   * @param {boolean} [options.addToStart] - Determines whether the release is
+   *   added to the top or bottom of the changelog. This defaults to 'true'
+   *   because new releases should be added to the top of the changelog. This
+   *   should be set to 'false' when parsing a changelog top-to-bottom.
+   * @param {string} [options.date] - An ISO-8601 formatted date, representing the
+   *   release date.
+   * @param {string} [options.status] - The status of the release (e.g.
+   *   'WITHDRAWN', 'DEPRECATED')
+   * @param {Version} options.version - The version of the current release,
+   *   which should be a [semver]{@link https://semver.org/spec/v2.0.0.html}-
+   *   compatible version.
+   */
+  addRelease({ addToStart = true, date, status, version }) {
+    if (!version) {
+      throw new Error('Version required');
+    } else if (semver.valid(version) === null) {
+      throw new Error(`Not a valid semver version: '${version}'`);
+    } else if (this._changes[version]) {
+      throw new Error(`Release already exists: '${version}'`);
+    }
+
+    this._changes[version] = {};
+    const newRelease = { version, date, status };
+    if (addToStart) {
+      this._releases.unshift(newRelease);
+    } else {
+      this._releases.push(newRelease);
+    }
+  }
+
+  /**
+   * Add a change to the changelog
+   *
+   * @param {Object} options
+   * @param {boolean} [options.addToStart] - Determines whether the change is
+   *   added to the top or bottom of the list of changes in this category. This
+   *   defaults to 'true' because changes should be in reverse-chronological
+   *   order. This should be set to 'false' when parsing a changelog top-to-
+   *   bottom.
+   * @param {string} options.category - The category of the change.
+   * @param {string} options.description - The description of the change.
+   * @param {Version} [options.version] - The version this change was released
+   *  in. If this is not given, the change is assumed to be unreleased.
+   */
+  addChange({ addToStart = true, category, description, version }) {
+    if (!category) {
+      throw new Error('Category required');
+    } else if (!orderedChangeCategories.includes(category)) {
+      throw new Error(`Unrecognized category: '${category}'`);
+    } else if (!description) {
+      throw new Error('Description required');
+    } else if (version !== undefined && !this._changes[version]) {
+      throw new Error(`Specified release version does not exist: '${version}'`);
+    }
+
+    const release = version
+      ? this._changes[version]
+      : this._changes[unreleased];
+
+    if (!release[category]) {
+      release[category] = [];
+    }
+    if (addToStart) {
+      release[category].unshift(description);
+    } else {
+      release[category].push(description);
+    }
+  }
+
+  /**
+   * Gets the metadata for all releases.
+   * @returns {Array<ReleaseMetadata>} The metadata for each release.
+   */
+  getReleases() {
+    return this._releases;
+  }
+
+  /**
+   * Gets the changes in the given release, organized by category.
+   * @param {Version} version - The version of the release being retrieved.
+   * @returns {ReleaseChanges} The changes included in the given released.
+   */
+  getReleaseChanges(version) {
+    return this._changes[version];
+  }
+
+  /**
+   * Gets all changes that have not yet been released
+   * @returns {ReleaseChanges} The changes that have not yet been released.
+   */
+  getUnreleasedChanges() {
+    return this._changes[unreleased];
+  }
+
+  /**
+   * The stringified changelog, formatted according to [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
+   * @returns {string} The stringified changelog.
+   */
+  toString() {
+    return `${changelogTitle}
+${changelogDescription}
+
+${stringifyReleases(this._releases, this._changes)}
+
+${stringifyLinkReferenceDefinitions(this._repoUrl, this._releases)}`;
+  }
+}
+
+module.exports = Changelog;
diff --git a/development/lib/changelog/constants.js b/development/lib/changelog/constants.js
new file mode 100644
index 000000000..c2b8ae008
--- /dev/null
+++ b/development/lib/changelog/constants.js
@@ -0,0 +1,68 @@
+/**
+ * Version string
+ * @typedef {string} Version - A [SemVer]{@link https://semver.org/spec/v2.0.0.html}-
+ *   compatible version string.
+ */
+
+/**
+ * Change categories.
+ *
+ * Most of these categories are from [Keep a Changelog]{@link https://keepachangelog.com/en/1.0.0/}.
+ * The "Uncategorized" category was added because we have many changes from
+ * older releases that would be difficult to categorize.
+ *
+ * @typedef {Record<string, string>} ChangeCategories
+ * @property {'Added'} Added - for new features.
+ * @property {'Changed'} Changed - for changes in existing functionality.
+ * @property {'Deprecated'} Deprecated - for soon-to-be removed features.
+ * @property {'Fixed'} Fixed - for any bug fixes.
+ * @property {'Removed'} Removed - for now removed features.
+ * @property {'Security'} Security - in case of vulnerabilities.
+ * @property {'Uncategorized'} Uncategorized - for any changes that have not
+ *   yet been categorized.
+ */
+
+/**
+ * @type {ChangeCategories}
+ */
+const changeCategories = {
+  Added: 'Added',
+  Changed: 'Changed',
+  Deprecated: 'Deprecated',
+  Fixed: 'Fixed',
+  Removed: 'Removed',
+  Security: 'Security',
+  Uncategorized: 'Uncategorized',
+};
+
+/**
+ * Change categories in the order in which they should be listed in the
+ * changelog.
+ *
+ * @type {Array<keyof ChangeCategories>}
+ */
+const orderedChangeCategories = [
+  'Uncategorized',
+  'Added',
+  'Changed',
+  'Deprecated',
+  'Removed',
+  'Fixed',
+  'Security',
+];
+
+/**
+ * The header for the section of the changelog listing unreleased changes.
+ * @typedef {'Unreleased'} Unreleased
+ */
+
+/**
+ * @type {Unreleased}
+ */
+const unreleased = 'Unreleased';
+
+module.exports = {
+  changeCategories,
+  orderedChangeCategories,
+  unreleased,
+};
diff --git a/development/lib/changelog/parseChangelog.js b/development/lib/changelog/parseChangelog.js
new file mode 100644
index 000000000..228da3635
--- /dev/null
+++ b/development/lib/changelog/parseChangelog.js
@@ -0,0 +1,84 @@
+const Changelog = require('./changelog');
+const { unreleased } = require('./constants');
+
+function truncated(line) {
+  return line.length > 80 ? `${line.slice(0, 80)}...` : line;
+}
+
+/**
+ * Constructs a Changelog instance that represents the given changelog, which
+ * is parsed for release and change informatino.
+ * @param {Object} options
+ * @param {string} options.changelogContent - The changelog to parse
+ * @param {string} options.repoUrl - The GitHub repository URL for the current
+ *   project.
+ * @returns {Changelog} A changelog instance that reflects the changelog text
+ *   provided.
+ */
+function parseChangelog({ changelogContent, repoUrl }) {
+  const changelogLines = changelogContent.split('\n');
+  const changelog = new Changelog({ repoUrl });
+
+  const unreleasedHeaderIndex = changelogLines.indexOf(`## [${unreleased}]`);
+  if (unreleasedHeaderIndex === -1) {
+    throw new Error(`Failed to find ${unreleased} header`);
+  }
+  const unreleasedLinkReferenceDefinition = changelogLines.findIndex((line) => {
+    return line.startsWith(`[${unreleased}]: `);
+  });
+  if (unreleasedLinkReferenceDefinition === -1) {
+    throw new Error(`Failed to find ${unreleased} link reference definition`);
+  }
+
+  const contentfulChangelogLines = changelogLines
+    .slice(unreleasedHeaderIndex + 1, unreleasedLinkReferenceDefinition)
+    .filter((line) => line !== '');
+
+  let mostRecentRelease;
+  let mostRecentCategory;
+  for (const line of contentfulChangelogLines) {
+    if (line.startsWith('## [')) {
+      const results = line.match(
+        /^## \[(\d+\.\d+\.\d+)\](?: - (\d\d\d\d-\d\d-\d\d))?(?: \[(\w+)\])?/u,
+      );
+      if (results === null) {
+        throw new Error(`Malformed release header: '${truncated(line)}'`);
+      }
+      mostRecentRelease = results[1];
+      mostRecentCategory = undefined;
+      const date = results[2];
+      const status = results[3];
+      changelog.addRelease({
+        addToStart: false,
+        date,
+        status,
+        version: mostRecentRelease,
+      });
+    } else if (line.startsWith('### ')) {
+      const results = line.match(/^### (\w+)$\b/u);
+      if (results === null) {
+        throw new Error(`Malformed category header: '${truncated(line)}'`);
+      }
+      mostRecentCategory = results[1];
+    } else if (line.startsWith('- ')) {
+      if (mostRecentCategory === undefined) {
+        throw new Error(`Category missing for change: '${truncated(line)}'`);
+      }
+      const description = line.slice(2);
+      changelog.addChange({
+        addToStart: false,
+        category: mostRecentCategory,
+        description,
+        version: mostRecentRelease,
+      });
+    } else if (mostRecentRelease === null) {
+      continue;
+    } else {
+      throw new Error(`Unrecognized line: '${truncated(line)}'`);
+    }
+  }
+
+  return changelog;
+}
+
+module.exports = { parseChangelog };
diff --git a/development/lib/changelog/updateChangelog.js b/development/lib/changelog/updateChangelog.js
new file mode 100644
index 000000000..2198b8f0a
--- /dev/null
+++ b/development/lib/changelog/updateChangelog.js
@@ -0,0 +1,163 @@
+const assert = require('assert').strict;
+const runCommand = require('../runCommand');
+const { parseChangelog } = require('./parseChangelog');
+const { changeCategories } = require('./constants');
+
+async function getMostRecentTag() {
+  const [mostRecentTagCommitHash] = await runCommand('git', [
+    'rev-list',
+    '--tags',
+    '--max-count=1',
+  ]);
+  const [mostRecentTag] = await runCommand('git', [
+    'describe',
+    '--tags',
+    mostRecentTagCommitHash,
+  ]);
+  assert.equal(mostRecentTag[0], 'v', 'Most recent tag should start with v');
+  return mostRecentTag;
+}
+
+async function getCommits(commitHashes) {
+  const commits = [];
+  for (const commitHash of commitHashes) {
+    const [subject] = await runCommand('git', [
+      'show',
+      '-s',
+      '--format=%s',
+      commitHash,
+    ]);
+
+    let prNumber;
+    let description = subject;
+
+    // Squash & Merge: the commit subject is parsed as `<description> (#<PR ID>)`
+    if (subject.match(/\(#\d+\)/u)) {
+      const matchResults = subject.match(/\(#(\d+)\)/u);
+      prNumber = matchResults[1];
+      description = subject.match(/^(.+)\s\(#\d+\)/u)[1];
+      // Merge: the PR ID is parsed from the git subject (which is of the form `Merge pull request
+      // #<PR ID> from <branch>`, and the description is assumed to be the first line of the body.
+      // If no body is found, the description is set to the commit subject
+    } else if (subject.match(/#\d+\sfrom/u)) {
+      const matchResults = subject.match(/#(\d+)\sfrom/u);
+      prNumber = matchResults[1];
+      const [firstLineOfBody] = await runCommand('git', [
+        'show',
+        '-s',
+        '--format=%b',
+        commitHash,
+      ]);
+      description = firstLineOfBody || subject;
+    }
+    // Otherwise:
+    // Normal commits: The commit subject is the description, and the PR ID is omitted.
+
+    commits.push({ prNumber, description });
+  }
+  return commits;
+}
+
+function getAllChangeDescriptions(changelog) {
+  const releases = changelog.getReleases();
+  const changeDescriptions = Object.values(
+    changelog.getUnreleasedChanges(),
+  ).flat();
+  for (const release of releases) {
+    changeDescriptions.push(
+      ...Object.values(changelog.getReleaseChanges(release.version)).flat(),
+    );
+  }
+  return changeDescriptions;
+}
+
+function getAllLoggedPrNumbers(changelog) {
+  const changeDescriptions = getAllChangeDescriptions(changelog);
+
+  const prNumbersWithChangelogEntries = [];
+  for (const description of changeDescriptions) {
+    const matchResults = description.match(/^\[#(\d+)\]/u);
+    if (matchResults === null) {
+      continue;
+    }
+    const prNumber = matchResults[1];
+    prNumbersWithChangelogEntries.push(prNumber);
+  }
+
+  return prNumbersWithChangelogEntries;
+}
+
+/**
+ * @typedef {import('./constants.js').Version} Version
+ */
+
+/**
+ * Update a changelog with any commits made since the last release. Commits for
+ * PRs that are already included in the changelog are omitted.
+ * @param {Object} options
+ * @param {string} options.changelogContent - The current changelog
+ * @param {Version} options.currentVersion - The current version
+ * @param {string} options.repoUrl - The GitHub repository URL for the current
+ *   project.
+ * @param {boolean} options.isReleaseCandidate - Denotes whether the current
+ *   project is in the midst of release preparation or not. If this is set, any
+ *   new changes are listed under the current release header. Otherwise, they
+ *   are listed under the 'Unreleased' section.
+ * @returns
+ */
+async function updateChangelog({
+  changelogContent,
+  currentVersion,
+  repoUrl,
+  isReleaseCandidate,
+}) {
+  const changelog = parseChangelog({ changelogContent, repoUrl });
+
+  // Ensure we have all tags on remote
+  await runCommand('git', ['fetch', '--tags']);
+  const mostRecentTag = await getMostRecentTag();
+  const commitsHashesSinceLastRelease = await runCommand('git', [
+    'rev-list',
+    `${mostRecentTag}..HEAD`,
+  ]);
+  const commits = await getCommits(commitsHashesSinceLastRelease);
+
+  const loggedPrNumbers = getAllLoggedPrNumbers(changelog);
+  const newCommits = commits.filter(
+    ({ prNumber }) => !loggedPrNumbers.includes(prNumber),
+  );
+
+  if (newCommits.length === 0) {
+    return undefined;
+  }
+
+  // Ensure release header exists, if necessary
+  if (
+    isReleaseCandidate &&
+    !changelog
+      .getReleases()
+      .find((release) => release.version === currentVersion)
+  ) {
+    changelog.addRelease({ currentVersion });
+  }
+
+  const newChangeEntries = newCommits.map(({ prNumber, description }) => {
+    if (prNumber) {
+      const prefix = `[#${prNumber}](${repoUrl}/pull/${prNumber})`;
+      return `${prefix}: ${description}`;
+    }
+    return description;
+  });
+
+  for (const description of newChangeEntries.reverse()) {
+    changelog.addChange({
+      version: isReleaseCandidate ? currentVersion : undefined,
+      category: changeCategories.Uncategorized,
+      description,
+    });
+  }
+
+  return changelog.toString();
+}
+
+module.exports = { updateChangelog };
diff --git a/package.json b/package.json
index 2fe6ed9d6..30c09015a 100644
--- a/package.json
+++ b/package.json
@@ -280,6 +280,7 @@
     "sass": "^1.32.4",
     "sass-loader": "^10.1.1",
     "selenium-webdriver": "4.0.0-alpha.7",
+    "semver": "^7.3.5",
     "serve-handler": "^6.1.2",
     "sinon": "^9.0.0",
     "source-map": "^0.7.2",
diff --git a/yarn.lock b/yarn.lock
index b47f81af3..28b7220d5 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -23334,6 +23334,13 @@ semver@^7.2.1, semver@^7.3.2, semver@^7.3.4:
   dependencies:
     lru-cache "^6.0.0"
 
+semver@^7.3.5:
+  version "7.3.5"
+  resolved "https://registry.yarnpkg.com/semver/-/semver-7.3.5.tgz#0b621c879348d8998e4b0e4be94b3f12e6018ef7"
+  integrity sha512-PoeGJYh8HK4BTO/a9Tf6ZG3veo/A7ZVsYrSA6J8ny9nb3B1VrpkuN+z9OE5wfE5p6H4LchYZsegiQgbJD94ZFQ==
+  dependencies:
+    lru-cache "^6.0.0"
+
 semver@~5.4.1:
   version "5.4.1"
   resolved "https://registry.yarnpkg.com/semver/-/semver-5.4.1.tgz#e059c09d8571f0540823733433505d3a2f00b18e"