Place carrots and onion in the cavity of the chicken. Rub the skin with butter and place in the slow cooker.
Cut lemon in half and squeeze juice all over the chicken. Cut juiced lemon halves into wheels and place around chicken. Sprinkle parsley, salt, poultry seasoning, thyme, and paprika over top.
Cover and cook on Low for 8 to 10 hours or High for 4 to 5 hours. An instant-read thermometer inserted into the thickest part of the thigh, near the bone, should read 165 degrees F (74 degrees C).