Place broccoli and salad dressing in a large resealable plastic bag, squeeze out excess air, and seal the bag. Marinate in the refrigerator for 8 hours, turning bag occasionally.
Preheat an outdoor grill for high heat and lightly oil the grate. Drain broccoli.
Grill broccoli on preheated grill until vegetables are tender and browned, turning occasionally, 5 to 7 minutes.