Cut chicken into eighths and place in a large bowl. Add Marinade to bowl and toss until chicken is completely covered. Cover bowl and refrigerate for 8 hours or overnight.
Preheat oven to 375°F.
Peel parsnip and carrots and cut into 1-inch chunks. Cut onion into similar 1-inch chunks and cut baby potatoes in half.
Add parsnips, carrots, onion, and potatoes to a bowl with olive oil, minced garlic, salt, and pepper. Toss to coat.
Lay out parsnips, carrots, onion, and potatoes on a sheet pan. Remove chicken from marinade and place pieces on top of root vegetables skin side up.
Roast for about 1 hour, or until the skin is golden brown, the juices run clear, and a thermometer inserted in the thickest part of the thigh away from bone registers 180°F