diff --git a/changelog.d/17318.misc b/changelog.d/17318.misc
new file mode 100644
index 0000000000..b0b21da23b
--- /dev/null
+++ b/changelog.d/17318.misc
@@ -0,0 +1 @@
+Make the release script create a release branch for Complement as well.
diff --git a/scripts-dev/release.py b/scripts-dev/release.py
index 9ea9b41505..5e519bb758 100755
--- a/scripts-dev/release.py
+++ b/scripts-dev/release.py
@@ -70,6 +70,7 @@ def cli() -> None:
             pip install -e .[dev]
 
       - A checkout of the sytest repository at ../sytest
+      - A checkout of the complement repository at ../complement
 
     Then to use:
 
@@ -112,10 +113,12 @@ def _prepare() -> None:
     # Make sure we're in a git repo.
     synapse_repo = get_repo_and_check_clean_checkout()
     sytest_repo = get_repo_and_check_clean_checkout("../sytest", "sytest")
+    complement_repo = get_repo_and_check_clean_checkout("../complement", "complement")
 
     click.secho("Updating Synapse and Sytest git repos...")
     synapse_repo.remote().fetch()
     sytest_repo.remote().fetch()
+    complement_repo.remote().fetch()
 
     # Get the current version and AST from root Synapse module.
     current_version = get_package_version()
@@ -208,7 +211,15 @@ def _prepare() -> None:
             "Which branch should the release be based on?", default=default
         )
 
-        for repo_name, repo in {"synapse": synapse_repo, "sytest": sytest_repo}.items():
+        for repo_name, repo in {
+            "synapse": synapse_repo,
+            "sytest": sytest_repo,
+            "complement": complement_repo,
+        }.items():
+            # Special case for Complement: `develop` maps to `main`
+            if repo_name == "complement" and branch_name == "develop":
+                branch_name = "main"
+
             base_branch = find_ref(repo, branch_name)
             if not base_branch:
                 print(f"Could not find base branch {branch_name} for {repo_name}!")
@@ -231,6 +242,12 @@ def _prepare() -> None:
         if click.confirm("Push new SyTest branch?", default=True):
             sytest_repo.git.push("-u", sytest_repo.remote().name, release_branch_name)
 
+        # Same for Complement
+        if click.confirm("Push new Complement branch?", default=True):
+            complement_repo.git.push(
+                "-u", complement_repo.remote().name, release_branch_name
+            )
+
     # Switch to the release branch and ensure it's up to date.
     synapse_repo.git.checkout(release_branch_name)
     update_branch(synapse_repo)
@@ -630,6 +647,9 @@ def _merge_back() -> None:
     else:
         # Full release
         sytest_repo = get_repo_and_check_clean_checkout("../sytest", "sytest")
+        complement_repo = get_repo_and_check_clean_checkout(
+            "../complement", "complement"
+        )
 
         if click.confirm(f"Merge {branch_name} → master?", default=True):
             _merge_into(synapse_repo, branch_name, "master")
@@ -643,6 +663,9 @@ def _merge_back() -> None:
         if click.confirm("On SyTest, merge master → develop?", default=True):
             _merge_into(sytest_repo, "master", "develop")
 
+        if click.confirm(f"On Complement, merge {branch_name} → main?", default=True):
+            _merge_into(complement_repo, branch_name, "main")
+
 
 @cli.command()
 def announce() -> None: