diff --git a/actions/ql/lib/change-notes/2026-07-27-merge-group-event-source.md b/actions/ql/lib/change-notes/2026-07-27-merge-group-event-source.md
new file mode 100644
index 000000000000..41b39b6c452f
--- /dev/null
+++ b/actions/ql/lib/change-notes/2026-07-27-merge-group-event-source.md
@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* GitHub Actions analysis now recognizes untrusted data in `github.event.merge_group` for workflows triggered by the `merge_group` event.
\ No newline at end of file
diff --git a/actions/ql/lib/ext/config/context_event_map.yml b/actions/ql/lib/ext/config/context_event_map.yml
index 541ac8b9a8f6..311ea7cf5481 100644
--- a/actions/ql/lib/ext/config/context_event_map.yml
+++ b/actions/ql/lib/ext/config/context_event_map.yml
@@ -19,6 +19,7 @@ extensions:
       - ["gollum", "github.event.changes"] 
       - ["pull_request_comment", "github.event.comment"] 
       - ["pull_request_comment", "github.event.pull_request"] 
+      - ["merge_group", "github.event.merge_group"]
       - ["pull_request_comment", "github.head_ref"] 
       - ["pull_request_comment", "github.event.changes"] 
       - ["pull_request_review", "github.event.pull_request"] 
diff --git a/actions/ql/test/query-tests/Security/CWE-094/.github/workflows/merge_group_code_injection.yml b/actions/ql/test/query-tests/Security/CWE-094/.github/workflows/merge_group_code_injection.yml
new file mode 100644
index 000000000000..02c9864bb7bf
--- /dev/null
+++ b/actions/ql/test/query-tests/Security/CWE-094/.github/workflows/merge_group_code_injection.yml
@@ -0,0 +1,12 @@
+on:
+  merge_group:
+    types: [checks_requested]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Use merge group payload
+        run: echo '${{ toJSON(github.event) }}'
+      - name: Use merge group head ref
+        run: echo '${{ github.event.merge_group.head_ref }}'
\ No newline at end of file
diff --git a/actions/ql/test/query-tests/Security/CWE-094/CodeInjectionCritical.expected b/actions/ql/test/query-tests/Security/CWE-094/CodeInjectionCritical.expected
index 9bf7e9aa56db..26f1046ed04f 100644
--- a/actions/ql/test/query-tests/Security/CWE-094/CodeInjectionCritical.expected
+++ b/actions/ql/test/query-tests/Security/CWE-094/CodeInjectionCritical.expected
@@ -400,6 +400,8 @@ nodes
 | .github/workflows/level0.yml:44:20:44:49 | github.event.issue.body | semmle.label | github.event.issue.body |
 | .github/workflows/level0.yml:69:35:69:66 | github.event.comment.body | semmle.label | github.event.comment.body |
 | .github/workflows/level1.yml:37:38:37:81 | github.event.workflow_run.head_branch | semmle.label | github.event.workflow_run.head_branch |
+| .github/workflows/merge_group_code_injection.yml:10:21:10:47 | toJSON(github.event) | semmle.label | toJSON(github.event) |
+| .github/workflows/merge_group_code_injection.yml:12:21:12:60 | github.event.merge_group.head_ref | semmle.label | github.event.merge_group.head_ref |
 | .github/workflows/priv_pull_request.yml:14:21:14:57 | github.event.pull_request.body | semmle.label | github.event.pull_request.body |
 | .github/workflows/pull_request_review.yml:7:19:7:56 | github.event.pull_request.title | semmle.label | github.event.pull_request.title |
 | .github/workflows/pull_request_review.yml:8:19:8:55 | github.event.pull_request.body | semmle.label | github.event.pull_request.body |
diff --git a/actions/ql/test/query-tests/Security/CWE-094/CodeInjectionMedium.expected b/actions/ql/test/query-tests/Security/CWE-094/CodeInjectionMedium.expected
index 4bbe7da0aaf3..020edd104b3b 100644
--- a/actions/ql/test/query-tests/Security/CWE-094/CodeInjectionMedium.expected
+++ b/actions/ql/test/query-tests/Security/CWE-094/CodeInjectionMedium.expected
@@ -400,6 +400,8 @@ nodes
 | .github/workflows/level0.yml:44:20:44:49 | github.event.issue.body | semmle.label | github.event.issue.body |
 | .github/workflows/level0.yml:69:35:69:66 | github.event.comment.body | semmle.label | github.event.comment.body |
 | .github/workflows/level1.yml:37:38:37:81 | github.event.workflow_run.head_branch | semmle.label | github.event.workflow_run.head_branch |
+| .github/workflows/merge_group_code_injection.yml:10:21:10:47 | toJSON(github.event) | semmle.label | toJSON(github.event) |
+| .github/workflows/merge_group_code_injection.yml:12:21:12:60 | github.event.merge_group.head_ref | semmle.label | github.event.merge_group.head_ref |
 | .github/workflows/priv_pull_request.yml:14:21:14:57 | github.event.pull_request.body | semmle.label | github.event.pull_request.body |
 | .github/workflows/pull_request_review.yml:7:19:7:56 | github.event.pull_request.title | semmle.label | github.event.pull_request.title |
 | .github/workflows/pull_request_review.yml:8:19:8:55 | github.event.pull_request.body | semmle.label | github.event.pull_request.body |
@@ -718,6 +720,8 @@ subpaths
 | .github/workflows/inter-job2.yml:45:20:45:53 | needs.job1.outputs.job_output | .github/workflows/inter-job2.yml:22:9:26:6 | Uses Step: source | .github/workflows/inter-job2.yml:45:20:45:53 | needs.job1.outputs.job_output | Potential code injection in $@, which may be controlled by an external user. | .github/workflows/inter-job2.yml:45:20:45:53 | needs.job1.outputs.job_output | ${{needs.job1.outputs.job_output}} |
 | .github/workflows/inter-job4.yml:44:20:44:53 | needs.job1.outputs.job_output | .github/workflows/inter-job4.yml:22:9:26:6 | Uses Step: source | .github/workflows/inter-job4.yml:44:20:44:53 | needs.job1.outputs.job_output | Potential code injection in $@, which may be controlled by an external user. | .github/workflows/inter-job4.yml:44:20:44:53 | needs.job1.outputs.job_output | ${{needs.job1.outputs.job_output}} |
 | .github/workflows/inter-job5.yml:45:20:45:53 | needs.job1.outputs.job_output | .github/workflows/inter-job5.yml:45:20:45:53 | needs.job1.outputs.job_output | .github/workflows/inter-job5.yml:45:20:45:53 | needs.job1.outputs.job_output | Potential code injection in $@, which may be controlled by an external user. | .github/workflows/inter-job5.yml:45:20:45:53 | needs.job1.outputs.job_output | ${{needs.job1.outputs.job_output}} |
+| .github/workflows/merge_group_code_injection.yml:10:21:10:47 | toJSON(github.event) | .github/workflows/merge_group_code_injection.yml:10:21:10:47 | toJSON(github.event) | .github/workflows/merge_group_code_injection.yml:10:21:10:47 | toJSON(github.event) | Potential code injection in $@, which may be controlled by an external user. | .github/workflows/merge_group_code_injection.yml:10:21:10:47 | toJSON(github.event) | ${{ toJSON(github.event) }} |
+| .github/workflows/merge_group_code_injection.yml:12:21:12:60 | github.event.merge_group.head_ref | .github/workflows/merge_group_code_injection.yml:12:21:12:60 | github.event.merge_group.head_ref | .github/workflows/merge_group_code_injection.yml:12:21:12:60 | github.event.merge_group.head_ref | Potential code injection in $@, which may be controlled by an external user. | .github/workflows/merge_group_code_injection.yml:12:21:12:60 | github.event.merge_group.head_ref | ${{ github.event.merge_group.head_ref }} |
 | .github/workflows/priv_pull_request.yml:14:21:14:57 | github.event.pull_request.body | .github/workflows/priv_pull_request.yml:14:21:14:57 | github.event.pull_request.body | .github/workflows/priv_pull_request.yml:14:21:14:57 | github.event.pull_request.body | Potential code injection in $@, which may be controlled by an external user. | .github/workflows/priv_pull_request.yml:14:21:14:57 | github.event.pull_request.body | ${{ github.event.pull_request.body }} |
 | .github/workflows/push.yml:7:19:7:57 | github.event.commits[11].message | .github/workflows/push.yml:7:19:7:57 | github.event.commits[11].message | .github/workflows/push.yml:7:19:7:57 | github.event.commits[11].message | Potential code injection in $@, which may be controlled by an external user. | .github/workflows/push.yml:7:19:7:57 | github.event.commits[11].message | ${{ github.event.commits[11].message }} |
 | .github/workflows/push.yml:8:19:8:62 | github.event.commits[11].author.email | .github/workflows/push.yml:8:19:8:62 | github.event.commits[11].author.email | .github/workflows/push.yml:8:19:8:62 | github.event.commits[11].author.email | Potential code injection in $@, which may be controlled by an external user. | .github/workflows/push.yml:8:19:8:62 | github.event.commits[11].author.email | ${{ github.event.commits[11].author.email }} |