McCormack won the prize at the National Irish Festival (the Feis Ceoil) in Dublin in 1903. Later he studied in Italy. He made his London operatic debut in 1907 at Covent Garden as Turiddu in Pietro Mascagni's Cavalleria rusticana. He appeared at the Manhattan Opera House, New York City, in 1909 as Alfredo in Giuseppe Verdi's La traviata. Subsequently he sang with opera companies in Chicago and Boston and with the Metropolitan Opera Company, New York City. In 1911 he toured Australia with Nellie Melba performing Italian opera. He later turned to the concert stage and became a fine singer of German lieder. Most popular with recital audiences were the Irish folk songs he invariably included in his programs. He was admired for the beauty of his voice and for his careful musicianship. He became a U.S. citizen in 1919 and was made a count in the papal peerage in 1928.