Heat the olive oil in your Dutch oven over medium-high heat. Add the beef stew meat cubes and brown them on all sides, about 5-7 minutes. Remove the beef and set aside.
In the same pot, add the chopped onion, diced carrots, and celery. Sauté until the vegetables soften, about 5 minutes. Stir in the minced garlic for the last minute until fragrant.
Return the browned beef to the pot. Add dried thyme, bay leaf, diced tomatoes, beef broth, and water. Stir to combine and bring to a gentle boil.
Once boiling, reduce heat to low and cover the pot. Let the soup simmer for about 1 hour, or until the beef is tender.
After the beef has softened, stir in the barley. Continue simmering the soup, uncovered, for an additional 30-40 minutes, or until the barley is tender and the soup has thickened slightly.
Remove the bay leaf, then taste and season with salt and pepper as needed. Serve hot with crusty bread or a simple green salad.