Place the beef stew meat, sweet potatoes, onion, carrots, and garlic into the slow cooker.
Add the beef broth, dried thyme, salt, and black pepper. Stir to combine everything evenly.
Cover and cook on low for 7 to 8 hours until the beef is tender.
Stir in the chopped kale during the final 30 minutes of cooking so it softens but stays bright.
Taste and adjust salt or pepper if needed before serving.