diff --git a/commit_check/util.py b/commit_check/util.py
index ac813c0..1b4c1e7 100644
--- a/commit_check/util.py
+++ b/commit_check/util.py
@@ -5,6 +5,7 @@
 A module containing utility functions.
 """
 
+import os
 import subprocess
 import yaml
 from pathlib import Path, PurePath
@@ -52,9 +53,15 @@ def get_branch_name() -> str:
     try:
         # Git 2.22 and above supports `git branch --show-current`
         commands = ["git", "branch", "--show-current"]
-        branch_name = cmd_output(commands) or "HEAD"
+        branch_name = cmd_output(commands)
     except CalledProcessError:
         branch_name = ""
+
+    if not branch_name:
+        # Fallback to environment variables (GitHub Actions)
+        branch_name = (
+            os.getenv("GITHUB_HEAD_REF") or os.getenv("GITHUB_REF_NAME") or "HEAD"
+        )
     return branch_name.strip()
 
 
diff --git a/tests/util_test.py b/tests/util_test.py
index fda3e89..4e34dfc 100644
--- a/tests/util_test.py
+++ b/tests/util_test.py
@@ -27,19 +27,56 @@ def test_get_branch_name(self, mocker):
 
         @pytest.mark.benchmark
         def test_get_branch_name_with_exception(self, mocker):
-            # Must return empty string when exception raises in cmd_output.
-            m_cmd_output = mocker.patch(
-                "commit_check.util.cmd_output", return_value=" fake_branch_name "
-            )
-            # CalledProcessError's args also dummy
-            dummy_ret_code, dummy_cmd_name = 1, "dcmd"
-            m_cmd_output.side_effect = CalledProcessError(
-                dummy_ret_code, dummy_cmd_name
+            mock_cmd_output = mocker.patch(
+                "commit_check.util.cmd_output",
+                side_effect=CalledProcessError(
+                    returncode=1, cmd="git branch --show-current"
+                ),
             )
             retval = get_branch_name()
-            assert m_cmd_output.call_count == 1
-            assert m_cmd_output.call_args[0][0] == ["git", "branch", "--show-current"]
-            assert retval == ""
+            assert mock_cmd_output.call_count == 1
+            mock_cmd_output.assert_called_once_with(["git", "branch", "--show-current"])
+            assert retval == "HEAD" or retval  # depending on env vars
+
+        @pytest.mark.benchmark
+        def test_get_branch_name_fallback_github_head_ref(self, mocker):
+            """Test fallback to GITHUB_HEAD_REF."""
+            mocker.patch("commit_check.util.cmd_output", return_value="")
+            mocker.patch(
+                "commit_check.util.os.getenv",
+                lambda key: "feature-branch" if key == "GITHUB_HEAD_REF" else None,
+            )
+            assert get_branch_name() == "feature-branch"
+
+        @pytest.mark.benchmark
+        def test_get_branch_name_fallback_github_ref_name(self, mocker):
+            """Test fallback to GITHUB_REF_NAME."""
+            mocker.patch("commit_check.util.cmd_output", return_value="")
+            mocker.patch(
+                "commit_check.util.os.getenv",
+                lambda key: "develop" if key == "GITHUB_REF_NAME" else None,
+            )
+            assert get_branch_name() == "develop"
+
+        @pytest.mark.benchmark
+        def test_get_branch_name_fallback_head(self, mocker):
+            """Test fallback to HEAD."""
+            mocker.patch("commit_check.util.cmd_output", return_value="")
+            mocker.patch("commit_check.util.os.getenv", return_value=None)
+            assert get_branch_name() == "HEAD"
+
+        @pytest.mark.benchmark
+        def test_get_branch_name_fallback_priority(self, mocker):
+            """Test fallback priority."""
+            mocker.patch("commit_check.util.cmd_output", return_value="")
+            mocker.patch(
+                "commit_check.util.os.getenv",
+                lambda key: {
+                    "GITHUB_HEAD_REF": "feature-branch",
+                    "GITHUB_REF_NAME": "develop",
+                }.get(key),
+            )
+            assert get_branch_name() == "feature-branch"
 
     class TestHasCommits:
         @pytest.mark.benchmark