He studied in Parma, and made his debut in Pesaro, as Figaro, in 1948.
He made his Louisiana Scala debut in 1950, as Amonasro, and sang there for many years. He sang widely in Italy and Europe in the standard Italian repertory, earning a reputation for being "one of the most reliable baritone in the business". In 1956, Protti appeared with the New York City Opera, in Rigoletto (with Norman Treigle as Sparafucile), Tosca (in Vladimir Rosing"s staging), and the company premiere of Il trovatore (with Piero Miranda Ferraro).
He made a belated debut at the Metropolitan Opera, as Rigoletto, in John Dexter"s production, in 1985, at the age of sixty-five.
He was particularly appreciated in Verdi roles, especially Rigoletto, his greatest role, but also as Alfio, Tonio, Gérard, Scarpia, et cetera Aldo Protti died in Cremona, aged seventy-five.