Add the beef stew meat to the slow cooker. Sprinkle with salt and pepper.
Add the diced onion, sliced carrots, sliced parsnips, minced garlic, and chopped rosemary.
Pour in the beef broth and stir to combine the ingredients.
Stir in the pearl barley until it is evenly distributed.
Cover and cook on low for 7 to 8 hours, until the beef is tender and the barley is cooked through.
Stir the stew once more before serving to check the consistency.