Place the flour, salt, and pepper in a bowl and toss the beef cubes until lightly coated.
Heat a skillet over medium heat and brown the beef in batches until the pieces are seared on all sides. Transfer the beef to the slow cooker.
Add the diced onion and minced garlic to the same skillet and cook for two minutes until the onion softens. Stir in the tomato paste and cook for one more minute.
Pour the Guinness into the skillet and scrape up the browned bits from the bottom. Let the liquid simmer for two minutes, then transfer everything to the slow cooker.
Add the beef broth, carrots, potatoes, thyme, and bay leaves to the slow cooker. Stir to combine.
Cover and cook on low for 8 hours until the beef is fork-tender and the potatoes are soft.
Remove the bay leaves. Sprinkle the chopped parsley over the stew before serving.