Place the beef stew meat, pearl barley, chopped onion, sliced carrots, cubed potatoes, and minced garlic into the slow cooker.
Pour in the beef broth and the can of diced tomatoes with their juices.
Add the dried thyme, salt, black pepper, and bay leaf, then stir everything to combine.
Cover and cook on low for 8 hours until the beef is tender and the barley is soft.
Remove the bay leaf, stir the stew, and serve hot.