In a slow cooker, combine beef stew meat, onion, beef broth, carrots, celery, thyme, salt, and pepper.
Cook on low for 6-8 hours, or until beef is tender.
Serve hot.
Notes
For a thicker soup, you can mix 1 tablespoon of cornstarch with 2 tablespoons of cold water and stir into the soup during the last 30 minutes of cooking.