Preheat the oven to 350 degrees F (175 degrees C).
Combine bison, bread crumbs, eggs, onion, Parmesan cheese, and black pepper in a large bowl. Fold in 1 cup marinara sauce. Pat into an 8x4-inch loaf pan using wet hands. Pour remaining marinara sauce over meatloaf.
Bake in the preheated oven until browned, about 1 hour. Let stand before cutting, about 20 minutes.