diff --git a/.github/update-release-branch.py b/.github/update-release-branch.py
index 9fb055b66..5e839dd55 100644
--- a/.github/update-release-branch.py
+++ b/.github/update-release-branch.py
@@ -8,8 +8,7 @@
 import datetime
 import os
 
-EMPTY_CHANGELOG = """
-# CodeQL Action and CodeQL Runner Changelog
+EMPTY_CHANGELOG = """# CodeQL Action and CodeQL Runner Changelog
 
 ## [UNRELEASED]
 
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 537eec7fc..0dc6b74ff 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,6 @@
 # CodeQL Action and CodeQL Runner Changelog
 
-## [UNRELEASED]
+## 1.0.0 - 31 May 2021
 
 - Add this changelog file. [#507](https://github.com/github/codeql-action/pull/507)
 - Improve grouping of analysis logs. Add a new log group containing a summary of metrics and diagnostics, if they were produced by CodeQL builtin queries. [#515](https://github.com/github/codeql-action/pull/515)