1. Place chicken in the slow cooker. Top with onion, carrots, celery, and garlic. Season with salt and pepper. Pour chicken broth over everything. Cook on high for three to four hours or low for six to eight hours.
2. Remove chicken from the pot and transfer to a cutting board. Shred the chicken with a fork and return to the slow cooker.
3. Add in egg noodles and stir. Cook on low for 10–15 minutes, until pasta is tender.