Add the beef stew meat, carrots, potatoes, parsnips, and onion to the slow cooker.
In a small bowl, whisk together the beef broth, tomato paste, Worcestershire sauce, minced garlic, dried thyme, salt, and black pepper until smooth.
Pour the broth mixture over the meat and vegetables in the slow cooker. Add the bay leaves on top.
Cover and cook on low for 8 hours or on high for 5 hours, until the beef is very tender and the vegetables are soft.
Remove and discard the bay leaves. Stir the stew gently, then sprinkle with fresh parsley before serving.