In a medium bowl, whisk balsamic vinegar, olive oil, honey, oregano, garlic, salt, and pepper until smooth.
Place pork loin in a sealable bag and pour marinade over top. Seal bag and allow pork to marinate in refrigerator 2 hours or up to 12 hours, tossing pork around in marinade occasionally to evenly coat.
When ready to grill, preheat grill to 375F. Remove pork from marinade and discard marinade. Pat pork loin dry and place on preheated grill. Turn pork occasionally until it reaches an internal temperature of 135F, about 10-15 minutes of cooking.
Remove pork from grill and place on a cutting board. Lightly tent with foil and allow to rest 10 minutes before carving. Once pork has rested, cut into slices and arrange on a serving plate.