It takes approximately four hours to cook a whole chicken in a slow cooker set on high. When using the low temperature setting, it takes six to eight hours to cook a whole chicken.
FoodSafety.gov recommends cooking whole chicken for 20 to 30 minutes per pound, so cooking times may vary based on the weight of the chicken. Using a meat thermometer is one way to tell if the chicken is fully cooked. Chicken is safe to eat when a meat thermometer registers 175 F to 180 F in the thickest part of the thigh or 165 F in the breast meat.