diff --git a/batch_runner.py b/batch_runner.py
index f2f00e0de1..af6dd75c1e 100644
--- a/batch_runner.py
+++ b/batch_runner.py
@@ -1246,21 +1246,21 @@ def main(
     # Validate required arguments
     if not dataset_file:
         print("❌ Error: --dataset_file is required")
-        return
-    
+        raise SystemExit(1)
+
     if not batch_size or batch_size < 1:
         print("❌ Error: --batch_size must be a positive integer")
-        return
-    
+        raise SystemExit(1)
+
     if not run_name:
         print("❌ Error: --run_name is required")
-        return
-    
+        raise SystemExit(1)
+
     # Parse provider preferences (comma-separated strings to lists)
     providers_allowed_list = [p.strip() for p in providers_allowed.split(",")] if providers_allowed else None
     providers_ignored_list = [p.strip() for p in providers_ignored.split(",")] if providers_ignored else None
     providers_order_list = [p.strip() for p in providers_order.split(",")] if providers_order else None
-    
+
     # Build reasoning_config from CLI flags
     # --reasoning_disabled takes priority, then --reasoning_effort, then default (medium)
     reasoning_config = None
@@ -1273,10 +1273,10 @@ def main(
         valid_efforts = ["none", "minimal", "low", "medium", "high", "xhigh", "max", "ultra"]
         if reasoning_effort not in valid_efforts:
             print(f"❌ Error: --reasoning_effort must be one of: {', '.join(valid_efforts)}")
-            return
+            raise SystemExit(1)
         reasoning_config = {"enabled": True, "effort": reasoning_effort}
         print(f"🧠 Reasoning effort: {reasoning_effort}")
-    
+
     # Load prefill messages from JSON file if provided
     prefill_messages = None
     if prefill_messages_file:
@@ -1285,12 +1285,12 @@ def main(
                 prefill_messages = json.load(f)
             if not isinstance(prefill_messages, list):
                 print("❌ Error: prefill_messages_file must contain a JSON array of messages")
-                return
+                raise SystemExit(1)
             print(f"💬 Loaded {len(prefill_messages)} prefill messages from {prefill_messages_file}")
         except Exception as e:
             print(f"❌ Error loading prefill messages: {e}")
-            return
-    
+            raise SystemExit(1)
+
     # Initialize and run batch runner
     try:
         runner = BatchRunner(
@@ -1317,12 +1317,12 @@ def main(
         )
 
         runner.run(resume=resume)
-    
+
     except Exception as e:
         print(f"\n❌ Fatal error: {e}")
         if verbose:
             traceback.print_exc()
-        return 1
+        raise SystemExit(1)
 
 
 if __name__ == "__main__":
diff --git a/tests/test_batch_runner_exit_code.py b/tests/test_batch_runner_exit_code.py
new file mode 100644
index 0000000000..7329c4622c
--- /dev/null
+++ b/tests/test_batch_runner_exit_code.py
@@ -0,0 +1,64 @@
+"""Regression tests for batch_runner process exit codes.
+
+Python Fire serializes the return value of the wrapped function but does not
+use it as the process exit code.  Before the fix, all of ``main``'s error paths
+returned ``0`` because a bare ``return`` or ``return 1`` was treated as the
+function result, not a non-zero exit status.
+"""
+
+import subprocess
+import sys
+from pathlib import Path
+
+import pytest
+
+
+REPO_ROOT = Path(__file__).parent.parent
+PYTHON = sys.executable
+
+
+def _run(*args):
+    return subprocess.run(
+        [PYTHON, "batch_runner.py", *args],
+        cwd=REPO_ROOT,
+        text=True,
+        capture_output=True,
+    )
+
+
+def test_missing_dataset_file_exits_nonzero():
+    result = _run("--run_name=test")
+    assert result.returncode == 1
+    assert "--dataset_file is required" in result.stdout
+
+
+def test_invalid_batch_size_exits_nonzero():
+    result = _run("--dataset_file=/tmp/data.jsonl", "--batch_size=-1", "--run_name=test")
+    assert result.returncode == 1
+    assert "--batch_size must be a positive integer" in result.stdout
+
+
+def test_invalid_reasoning_effort_exits_nonzero():
+    result = _run(
+        "--dataset_file=/tmp/data.jsonl",
+        "--batch_size=1",
+        "--run_name=test",
+        "--reasoning_effort=invalid",
+    )
+    assert result.returncode == 1
+    assert "--reasoning_effort must be one of" in result.stdout
+
+
+def test_invalid_prefill_messages_file_exits_nonzero(tmp_path):
+    bad_prefill = tmp_path / "prefill.json"
+    bad_prefill.write_text("not json", encoding="utf-8")
+    result = _run(
+        "--dataset_file=/tmp/data.jsonl",
+        "--batch_size=1",
+        "--run_name=test",
+        f"--prefill_messages_file={bad_prefill}",
+    )
+    assert result.returncode == 1
+    assert "Error loading prefill messages" in result.stdout
+
+