Toss the beef cubes with the flour, salt, and pepper in a bowl until evenly coated.
Heat a large skillet over medium heat and brown the beef in batches, then transfer the pieces to the slow cooker.
Add the onions, carrots, potatoes, and garlic to the slow cooker with the beef.
Pour in the Guinness and beef broth, then stir in the tomato paste and thyme until the tomato paste dissolves.
Add the bay leaves, cover the slow cooker, and cook on low for 8 hours.
Remove the bay leaves before serving and sprinkle with chopped parsley.