Place chicken breasts, carrots, celery, onion, and garlic in the slow cooker.
Pour chicken broth over everything and add bay leaves, thyme, salt, and pepper.
Cover and cook on low for 6-7 hours or high for 3-4 hours until chicken is fully cooked and vegetables are tender.
Remove chicken from slow cooker and shred with two forks, then return to the pot.
Add egg noodles, cover, and cook on high for an additional 30 minutes until noodles are tender.
Remove bay leaves, stir in fresh parsley, and adjust seasoning to taste before serving.