Heat olive oil in a large Dutch oven or soup pot over medium-high heat until shimmering. Working in batches to avoid crowding, brown the beef chuck on all sides for 8-10 minutes total, then transfer to a plate. Don't rush this step because the browned bits add incredible depth to your finished dish.
Add diced onion to the same pot and sauté for 3-4 minutes until softened and fragrant. Stir in minced garlic and cook for another 30 seconds, being careful not to burn it because burnt garlic turns bitter immediately.
Return the beef to the pot along with carrots, celery, mushrooms, and pearl barley. Stir everything together for 1-2 minutes to coat with the oil and aromatics that now coat the bottom of the pot.
Pour in beef broth and diced tomatoes, then add bay leaves, thyme, and oregano, stirring well to combine. Bring to a boil, then immediately reduce heat to low and simmer covered for 40-45 minutes until the beef is tender and barley is cooked through. The beef and barley soup recipe transforms completely during this gentle cooking time.
Taste the broth and season generously with salt and pepper until it's absolutely delicious. Remove bay leaves before serving this comfort soup to family and friends who'll ask for the recipe immediately.