Place the beef stew meat in the bottom of the slow cooker.
Add the pearl barley, carrots, parsnips, potatoes, and onion on top of the beef.
Pour in the beef broth and add the minced garlic, dried thyme, and bay leaf.
Season with salt and pepper, then stir everything together gently.
Cover and cook on low for 8 hours until the beef is tender and the barley is cooked through.
Remove the bay leaf before serving.