Add the beef stew meat to the slow cooker first.
Layer the sliced mushrooms, pearl onions, chopped carrots, and cubed potatoes over the beef.
In a mixing bowl, whisk together the Guinness, beef broth, tomato paste, minced garlic, dried thyme, salt, and black pepper until smooth.
Pour the liquid mixture over the meat and vegetables in the slow cooker.
Place the bay leaves on top.
Cover and cook on low for 8 hours.
Remove the bay leaves before serving.