Pat beef cubes dry with paper towels and season generously with salt and pepper.
Heat olive oil in a large Dutch oven or soup pot over medium-high heat. Brown beef in batches, about 3-4 minutes per side. Don't overcrowd the pot! Transfer browned beef to a plate.
In the same pot, add onion, carrots, and celery. Sauté for 5-6 minutes until vegetables begin to soften. Add garlic and cook for another minute until fragrant.
Return the beef to the pot along with any accumulated juices. Add beef broth, barley, bay leaves, and thyme. Stir to combine.
Bring to a boil, then reduce heat to low. Cover and simmer for 75-90 minutes, stirring occasionally, until beef is tender and barley is cooked through.
Remove bay leaves. Taste and adjust seasoning with salt and pepper as needed.
Ladle into bowls and garnish with fresh parsley. Serve with crusty bread for the ultimate cozy meal!