Heat the olive oil in a skillet over medium heat. Add the beef stew meat and cook until browned on all sides, about 5 minutes.
Transfer the browned beef to the slow cooker. Add the onion, garlic, carrots, parsnips, potatoes, and barley.
Pour in the beef broth and stir in the thyme, bay leaves, salt, and pepper.
Cover and cook on low for 8 hours or until the beef is tender and the barley is soft.
Remove the bay leaves before serving.