Marinate the Chicken: In a bowl, mix balsamic vinegar, olive oil, garlic, thyme, salt, and pepper. Coat the chicken evenly. Let it sit for 30 minutes to 4 hours.
Preheat Oven: Heat oven to 400°F (200°C).
Prepare for Roasting: Place chicken on a baking sheet. Scatter grapes around the chicken. Drizzle a little olive oil over everything.
Roast the Chicken: Bake for 25-30 minutes, depending on thickness. Toss grapes halfway through for even roasting.
Check Doneness: Chicken is cooked when internal temperature reaches 165°F (74°C).
Serve: Sprinkle fresh herbs on top. Pair with mashed potatoes, roasted vegetables, or a light salad.