Amato was one of the outstanding baritones of his day, with the easy, almost tenor-like upper register that marks the successful Verdi baritone, and an exceptional legato line. He was also a powerful dramatic figure, effective in both comic and serious roles. While best known for his performances in Italian opera, he also appeared in the Italian premiere of Debussy's Pelléas et Mélisande and sang such Wagner roles as Kurwenal in Tristan und Isolde and Gurnemanz in Parsifal.
He studied at the San Pietro a Majella conservatory in Naples and made his debut at the Bellini Theater in 1900 as Germont in Verdi's La Traviata. In 1904, he debuted at Covent Garden as part of the San Carlo touring company. In 1908, he debuted, again as Germont, at the Metropolitan Opera, where he was soon established as a leading baritone. He sang there regularly until 1921. In 1910, he created the role of Jack Rance in Puccini's La fanciulla del West, opposite Enrico Caruso. In 1913, he was the first performer in the title role of Damrosch's Cyrano de Bergerac, and, two years later, created Napoleon in Giordano's comic opera Madame Sans-Gene. In 1933, he retired from the stage, becoming the head of the vocal and opera department at the University of Louisiana in 1935. He taught there until his death in 1942.