Heat a tablespoon of oil in a large skillet over medium-high heat. Add the beef chunks and sear until browned on all sides, about 5 minutes. Transfer the beef to your slow cooker.
Add diced onions, chopped carrots, and sliced celery to the skillet. Sauté for about 3-4 minutes until the vegetables are slightly softened and fragrant. Transfer the vegetables to the slow cooker with the beef.
Pour in the beef broth and stir in the soy sauce and thyme. Mix gently to combine and loosen any browned bits from the skillet, then pour everything into the slow cooker.
Cover the slow cooker and cook on low for 4 to 6 hours, or until the beef is tender and the vegetables are cooked through.
About 30 minutes before serving, add the rinsed barley to the slow cooker. Stir well, re-cover, and continue cooking on low until the barley is tender and the soup is slightly thickened.
Once ready, taste the soup and adjust seasoning with salt and pepper as desired. Let it rest for a few minutes to allow flavors to meld.
Spoon the hearty beef and barley soup into bowls, showcasing the rustic chunks of meat, the chewy barley, and vibrant vegetables in a savory broth. Serve hot and enjoy!