diff --git a/actions/setup/js/push_signed_commits.cjs b/actions/setup/js/push_signed_commits.cjs
index b87caa43b5b..31643b5d842 100644
--- a/actions/setup/js/push_signed_commits.cjs
+++ b/actions/setup/js/push_signed_commits.cjs
@@ -184,9 +184,23 @@ async function pushSignedCommits({ githubClient, owner, repo, branch, baseRef, c
   // so skip it entirely and fall directly through to git push.
   if (!baseRef) {
     core.info(`pushSignedCommits: empty baseRef detected (orphan branch first push), using git push directly for branch ${branch}`);
-    const headSha = await pushBranchAndResolveHead({ branch, cwd, gitAuthEnv });
-    core.info(`pushSignedCommits: git push completed for orphan branch, HEAD=${headSha}`);
-    return headSha;
+    try {
+      const headSha = await pushBranchAndResolveHead({ branch, cwd, gitAuthEnv });
+      core.info(`pushSignedCommits: git push completed for orphan branch, HEAD=${headSha}`);
+      return headSha;
+    } catch (pushErr) {
+      const pushErrMsg = pushErr instanceof Error ? pushErr.message : String(pushErr);
+      throw new Error(
+        `pushSignedCommits: failed to push orphan branch '${branch}' (first commit). ` +
+          `If the repository requires signed commits, the branch must be seeded manually with a signed commit before this workflow can push to it. ` +
+          `Run the following commands locally (requires a GPG key configured with Git):\n\n` +
+          `  git switch --orphan ${branch}\n` +
+          `  git commit --allow-empty -S -m "Initialize ${branch}"\n` +
+          `  git push origin ${branch}\n\n` +
+          `Original error: ${pushErrMsg}`,
+        { cause: pushErr }
+      );
+    }
   }
 
   // Collect the commits introduced (oldest-first) using topological order to ensure
diff --git a/actions/setup/js/push_signed_commits.test.cjs b/actions/setup/js/push_signed_commits.test.cjs
index 3faf33a376b..f07d65bd27b 100644
--- a/actions/setup/js/push_signed_commits.test.cjs
+++ b/actions/setup/js/push_signed_commits.test.cjs
@@ -645,6 +645,49 @@ describe("push_signed_commits integration tests", () => {
       // Return value should be the HEAD SHA.
       expect(result).toBe(expectedSha);
     });
+
+    it("should throw with manual seeding instructions when orphan-branch git push fails", async () => {
+      // Simulate a repo where "Require signed commits" is enforced. The orphan-branch
+      // first push uses git push directly, which will be rejected by the remote with
+      // GH013. We simulate this by using a bare repo that refuses the push via a
+      // pre-receive hook.
+      execGit(["checkout", "--orphan", "experiments/signed-required"], { cwd: workDir });
+      execGit(["read-tree", "--empty"], { cwd: workDir });
+      fs.writeFileSync(path.join(workDir, "state.json"), JSON.stringify({ runs: 1 }));
+      execGit(["add", "state.json"], { cwd: workDir });
+      execGit(["commit", "-m", "Initial experiment state"], { cwd: workDir });
+
+      // Install a pre-receive hook in the bare repo that mimics GH013 by rejecting all pushes.
+      const hooksDir = path.join(bareDir, "hooks");
+      fs.mkdirSync(hooksDir, { recursive: true });
+      const hookPath = path.join(hooksDir, "pre-receive");
+      fs.writeFileSync(hookPath, "#!/bin/sh\necho 'remote: error: GH013: Repository rule violations found.' >&2\necho 'remote: - Commits must have verified signatures.' >&2\nexit 1\n");
+      fs.chmodSync(hookPath, "0755");
+
+      // Use the real exec so git push actually runs and hits the hook.
+      global.exec = makeRealExec(workDir);
+      const githubClient = makeMockGithubClient();
+
+      let thrownErr;
+      try {
+        await pushSignedCommits({
+          githubClient,
+          owner: "test-owner",
+          repo: "test-repo",
+          branch: "experiments/signed-required",
+          baseRef: "",
+          cwd: workDir,
+        });
+      } catch (err) {
+        thrownErr = err;
+      }
+      expect(thrownErr).toBeDefined();
+      expect(thrownErr.message).toContain("failed to push orphan branch");
+      expect(thrownErr.message).toContain("git switch --orphan experiments/signed-required");
+      expect(thrownErr.message).toContain("git commit --allow-empty -S");
+      expect(thrownErr.message).toContain("git push origin experiments/signed-required");
+      expect(thrownErr.message).toContain("signed commits");
+    });
   });
 
   // ──────────────────────────────────────────────────────