Sear the Meat: Heat olive oil in a pan over medium-high heat. Brown the roast on all sides to lock in juices and flavor.
Prepare the Slow Cooker: Place chopped onions, garlic, carrots, and celery at the bottom of the slow cooker.
Add Roast and Seasoning: Place seared roast on top of vegetables. Pour in beef stock and Worcestershire sauce. Sprinkle thyme, rosemary, salt, and pepper.
Slow Cook: Cover and cook on low for 8–10 hours or high for 4–6 hours until meat is tender and easily shredded.
Serve: Slice against the grain and serve with vegetables. Strain cooking liquid for gravy if desired.