Heat the olive oil in a large pot over medium-high heat. Season the beef cubes with salt and pepper, then add to the pot. Brown the beef on all sides, then remove and set aside.
In the same pot, add the onion, garlic, carrots, and celery. Cook until the vegetables are softened, about 5 minutes.
Return the beef to the pot. Add the barley, beef broth, bay leaf, and thyme. Bring to a boil, then reduce heat to low and simmer, covered, for about 1.5 to 2 hours, or until the beef is tender and the barley is cooked.
Remove the bay leaf. Adjust seasoning with salt and pepper. Serve hot, garnished with fresh parsley.