He was the head of the costume department at MGM for many years, and worked on 200 films from 1924 to 1948; he was credited by his last name, "Costumes by Adrian." (Gilbert was his father's name, which he adopted.) Unlike other studio department heads, however, he took a hands-on approach to his work, sketching costume designs for his staff to create.
He was born in Connecticut, and attended the New York School of Fine Arts. He began his career while still a student, designing some costumes for George White's Scandals in 1921. After moving to Hollywood he worked for Natasha Rambova and Rudolf Valentino, and Cecil B. DeMille. Adrian worked at MGM from 1928 to 1942. He ran his own fashion business outside of the movies, with salons in New York and Beverly Hills.
Though arguably the most prominent costume designer in films in his era, he never won an Academy Award. He did win a Tony Award, posthumously, in 1961, for his costumes for Camelot.