Layer the sliced carrots, celery, and onion in the base of your slow cooker.
Arrange the chicken thighs evenly on top of the vegetables.
In a separate bowl, combine chicken stock, au jus mix, chicken gravy mix, garlic powder, onion powder, and black pepper, whisking until fully blended.
Pour the mixture evenly over the chicken and veggies.
Cover the slow cooker and set to LOW, cooking for 6 hours, or use HIGH and cook for 4 hours, until chicken is cooked through and easily shredded with a fork.
Optionally sprinkle fresh parsley on top before serving.
Serve warm alongside mashed potatoes, egg noodles, or rice for a cozy meal.