Add the beef, onion, carrots, potatoes, and garlic to the slow cooker.
In a mixing bowl, whisk the Guinness, beef broth, tomato paste, thyme, salt, and pepper until smooth.
Pour the liquid mixture over the beef and vegetables in the slow cooker.
Place the bay leaves on top, then cover and cook on low for 8 hours.
Remove the bay leaves and stir the stew gently before serving.
Spoon into bowls and sprinkle with the chopped parsley.