diff --git a/docs/github-action.md b/docs/github-action.md
index 5424b7cc..a7013ee7 100644
--- a/docs/github-action.md
+++ b/docs/github-action.md
@@ -11,6 +11,15 @@ Follow the [Create the GitHub App](deploy.md#create-the-github-app) guide to cre
 Running a full-sync with `safe-settings` can be done via `npm run full-sync`. This requires installing Node, such as with [actions/setup-node](https://github.com/actions/setup-node) (see example below). When doing so, the appropriate environment variables must be set (see the [Environment variables](#environment-variables) document for more details).
 
 
+### GitHub Action Mode
+
+When running safe-settings in GitHub Actions, you can enable `GITHUB_ACTION_MODE=true` to automatically post PR comments using the built-in GitHub Actions environment variables. When this mode is enabled:
+
+- `GITHUB_REPOSITORY` (format: `owner/repo`) - automatically injected by GitHub Actions
+- `GITHUB_REF` (format: `refs/pull/123/merge` for PRs) - automatically injected by GitHub Actions
+
+These variables are used to identify the PR and post comments without additional configuration.
+
 ### Example GHA Workflow
 The below example uses the GHA "cron" feature to run a full-sync every 4 hours. While not required, this example uses the `.github` repo as the `admin` repo (set via `ADMIN_REPO` env var) and the safe-settings configurations are stored in the `safe-settings/` directory (set via `CONFIG_PATH` and `DEPLOYMENT_CONFIG_FILE`).
 
@@ -54,4 +63,7 @@ jobs:
           ADMIN_REPO: .github
           CONFIG_PATH: safe-settings
           DEPLOYMENT_CONFIG_FILE: ${{ github.workspace }}/safe-settings/deployment-settings.yml
+          # Enable GitHub Action mode to post PR comments using built-in env vars
+          # GITHUB_REPOSITORY and GITHUB_REF are automatically injected by GitHub Actions
+          GITHUB_ACTION_MODE: true
 ```
diff --git a/lib/env.js b/lib/env.js
index 94c0ea74..32dd56cd 100644
--- a/lib/env.js
+++ b/lib/env.js
@@ -6,5 +6,9 @@ module.exports = {
   CREATE_PR_COMMENT: process.env.CREATE_PR_COMMENT || 'true',
   CREATE_ERROR_ISSUE: process.env.CREATE_ERROR_ISSUE || 'true',
   BLOCK_REPO_RENAME_BY_HUMAN: process.env.BLOCK_REPO_RENAME_BY_HUMAN || 'false',
-  FULL_SYNC_NOP: process.env.FULL_SYNC_NOP === 'true'
+  FULL_SYNC_NOP: process.env.FULL_SYNC_NOP === 'true',
+  GITHUB_ACTION_MODE: process.env.GITHUB_ACTION_MODE === 'true',
+  // GitHub Actions built-in variables
+  GITHUB_REPOSITORY: process.env.GITHUB_REPOSITORY || '', // format: owner/repo
+  GITHUB_REF: process.env.GITHUB_REF || '' // format: refs/pull/123/merge for PRs
 }
diff --git a/lib/settings.js b/lib/settings.js
index 8d9e07b2..e7f227b1 100644
--- a/lib/settings.js
+++ b/lib/settings.js
@@ -259,8 +259,7 @@ class Settings {
 
     const renderedCommentMessage = await eta.renderString(commetMessageTemplate, stats)
 
-    if (env.CREATE_PR_COMMENT === 'true') {
-      const summary = `
+    const summary = `
 #### :robot: Safe-Settings config changes detected:
 
 ${this.results.reduce((x, y) => {
@@ -283,6 +282,29 @@ ${this.results.reduce((x, y) => {
       }, table)}
 `
 
+    // In GITHUB_ACTION_MODE, post a PR comment using GitHub Actions built-in env vars
+    if (env.GITHUB_ACTION_MODE && env.GITHUB_REPOSITORY && env.GITHUB_REF) {
+      const prMatch = env.GITHUB_REF.match(/refs\/pull\/(\d+)\//)
+      if (prMatch) {
+        const [owner, repo] = env.GITHUB_REPOSITORY.split('/')
+        const prNumber = parseInt(prMatch[1], 10)
+
+        try {
+          await this.github.issues.createComment({
+            owner,
+            repo,
+            issue_number: prNumber,
+            body: summary.length > 55536 ? `${summary.substring(0, 55536)}... (too many changes to report)` : summary
+          })
+          this.log.info(`PR comment posted to ${owner}/${repo}#${prNumber}`)
+        } catch (e) {
+          this.log.error(`Failed to post PR comment: ${e.message}`)
+        }
+      }
+      return
+    }
+
+    if (env.CREATE_PR_COMMENT === 'true') {
       const pullRequest = payload.check_run.check_suite.pull_requests[0]
 
       await this.github.issues.createComment({
@@ -978,6 +1000,7 @@ ${this.results.reduce((x, y) => {
     }
     return typeof obj[Symbol.iterator] === 'function'
   }
+
 }
 
 function prettify (obj) {