Heat olive oil in a large pot over medium heat.
Add the beef cubes and sear until browned on all sides.
Remove beef and set aside. In the same pot, add onions, carrots, and celery.
Sauté until the vegetables are tender, about 5 minutes.
Stir in garlic and cook for another minute.
Return beef to the pot and add barley, broth, and diced tomatoes.
Season with thyme, salt, and pepper.
Bring the mixture to a boil, then reduce heat to low.
Cover and simmer for 1 hour, stirring occasionally.
Taste and adjust seasoning if needed before serving.