Load the slow cooker with broth, carrots, celery, onion, and garlic.
Season with thyme, parsley, salt, and pepper. Stir to combine.
Nestle chicken breasts into the mixture, submerging them in the broth.
Cover and cook on Low for 6 hours, or High for 3 to 4 hours.
Transfer chicken to a board and shred with two forks. Skim broth if needed.
Stir in egg noodles. Cook on High until tender, about 15 to 20 minutes.
Return shredded chicken to the pot. Add lemon juice and fresh parsley.
Taste and adjust salt or pepper. Ladle into bowls and serve warm.