Both looks were provided by the titular Italian label.
Gaga and Leto were joined on the carpet by co-star Adam Driver, who looked sharp in a navy suit and tie by Burberry.
Gaga got a leg up in her look, which she styled with thigh-high fishnet stockings and her signature platform heels.
Cynthia Erivo picked a distressed navy knit set.
Gaga and Driver snuck in a cuddle on the carpet.
Salma Hayek, whose husband, François Henri Pinault, is the CEO of Gucci parent company Kering glittered in a golden gown by the label.
Driver and Gaga play Maurizio Gucci and Patrizia Reggiani in the film.
Driver is the face (and body) of Burberry's Hero fragrance.
Gaga spread her wings for photographers.