Heat the vegetable oil in a large pot over medium-high heat.
Season the beef chuck with salt and pepper, then add it to the pot in batches.
Remove the browned beef and set it aside; then add the diced onion, carrot, and celery.
Stir in the minced garlic and cook for an additional minute until fragrant.
Add the tomato paste and stir to combine, cooking for another 2–3 minutes.
Return the beef to the pot and pour in the Guinness beer, scraping the bottom to release any stuck bits.
Pour in the beef stock, add thyme and bay leaves, and bring to a boil.
Reduce the heat and let the stew simmer gently for about 2–3 hours, or until the beef is tender.
Taste and adjust the seasoning with salt and pepper, then remove the bay leaves.
Serve hot, garnished with fresh parsley over each bowl.