Place the beef stew meat, sliced mushrooms, chopped onion, sliced carrots, and minced garlic into the slow cooker.
Add the pearl barley, beef broth, dried thyme, salt, black pepper, and Worcestershire sauce.
Stir everything together until the ingredients are evenly combined.
Cover and cook on low for 7 to 8 hours, until the beef is tender and the barley is soft.
Stir once more, then sprinkle with chopped fresh parsley before serving.