Toss the beef cubes with flour, salt, and pepper in a bowl until evenly coated.
Heat 2 tablespoons of oil in a large Dutch oven over medium-high heat.
Sear the beef in batches until browned on all sides, then remove to a side plate.
Add the remaining tablespoon of oil to the pot and sauté the onion until softened, approximately 5 minutes.
Add the garlic and cook for 60 seconds until fragrant.
Deglaze the pot with the Guinness, using a wooden spoon to scrape all browned bits (fond) from the bottom.
Whisk in the beef stock, tomato paste, Worcestershire sauce, and brown sugar.
Return the beef and any accumulated juices to the pot; add the thyme, rosemary, and bay leaves.
Bring to a simmer, then reduce heat to low, cover, and braise for 90 minutes.
Incorporate the carrots and potatoes, cover, and continue to simmer for 30 to 40 minutes until the beef and vegetables are fork-tender.
Remove the herb sprigs and bay leaves before serving.