Preheat oven to 350°F and grease a 9x13-inch baking dish.
Spread uncooked rice evenly in bottom of prepared dish.
In a bowl, whisk together chicken broth and cream of chicken soup, then pour over rice.
Sprinkle frozen vegetables, onion, and celery over the rice mixture.
Season chicken thighs with poultry seasoning, garlic powder, salt, and pepper, then arrange on top of rice.
Dot butter pieces over chicken and rice.
Cover tightly with aluminum foil and bake for 60 minutes.
Remove foil and bake uncovered for 15 minutes more until chicken is golden and rice is tender.