Place the beef stew meat in the bottom of the slow cooker.
Add the sliced carrots, cubed potatoes, sliced parsnip, diced onion, and minced garlic on top of the meat.
Sprinkle the pearl barley, dried thyme, salt, and black pepper over the vegetables.
Stir the tomato paste into the beef broth until it dissolves, then pour the mixture into the slow cooker.
Cover and cook on low for 8 hours until the beef is tender and the barley is cooked through.
Stir once before serving to combine everything evenly.