Heat the olive oil in a skillet over medium heat. Add the beef stew meat and brown on all sides for about 5 minutes.
Transfer the browned beef to the slow cooker. Add the carrots, celery, onion, potatoes, and garlic.
Pour in the beef broth. Stir in the thyme, bay leaf, salt, and black pepper.
Cover and cook on low for 6 hours.
Stir in the rinsed quinoa. Cover and cook for 30 more minutes until the quinoa is tender and the beef is soft.
Remove the bay leaf before serving.