Place the beef stew meat into the slow cooker, spreading it out evenly to ensure good contact with the heat.
Add the rinsed pearl barley, chopped carrots, diced onion, and minced garlic over the beef, distributing evenly.
Pour in the beef broth, ensuring that all ingredients are submerged, then sprinkle with dried thyme and tuck in the bay leaf.
Season with salt and pepper to taste, then cover the slow cooker with its lid and set to low heat.
Let the soup simmer undisturbed for about 6 hours, until the beef is tender and the barley has absorbed the flavorful broth, creating a thick, hearty consistency.
Remove and discard the bay leaf, then give the soup a gentle stir to combine all the flavors and check seasoning adjustments.
Serve the soup hot, ladled into bowls, with a slice of crusty bread if desired. Enjoy the rustic, tender bites and savory aroma.