If you have a few extra minutes, heat olive oil in a skillet over medium-high heat and sear the chicken breasts for 2 minutes per side. This is optional but adds deeper flavor to the finished soup.
Place the chicken breasts, carrots, celery, onion, and garlic into the bottom of a 6-quart or larger crockpot.
Pour in the chicken broth, then add the thyme, parsley, bay leaf, salt, and pepper. Stir gently to combine.
Cover and cook on low for 6 to 7 hours, or on high for 3 to 4 hours, until the chicken is fully cooked and the vegetables are tender.
Remove the chicken breasts and shred them with two forks on a cutting board or plate.
Return the shredded chicken to the crockpot. Discard the bay leaf.
Stir in the egg noodles, cover, and cook on high for an additional 15 to 20 minutes, until the noodles are tender but not mushy.
Taste and adjust the seasoning with more salt and pepper as needed.
Ladle into bowls, garnish with a sprinkle of fresh parsley, and serve warm.