Fill a large saucepan with lightly salted water and bring to a rolling boil over high heat. Once the water is boiling, stir in the macaroni and return to a boil. Cook the pasta uncovered, stirring occasionally, until the pasta has cooked through but is still firm to the bite, about 8 minutes. Drain well in a colander set in the sink. Transfer the macaroni to a bowl and cool in the refrigerator.
In a large bowl, lightly toss the tuna with celery, onion and about 1 cup mayonnaise until combined then stir in the remaining mayonnaise, macaroni, olives and grape tomatoes. Season to taste with salt and pepper. Let the salad chill in refrigerator 1 hour.