Add the beef stew meat, onion, carrots, and celery to the slow cooker.
Pour in the beef broth and diced tomatoes.
Stir in the kidney beans, black beans, and pinto beans.
Add the garlic powder, oregano, salt, and black pepper. Stir everything to combine.
Cover and cook on low for 7 to 8 hours until the beef is tender.
Stir once more before serving.