As a boy, Milnes learned the piano and violin at home, and played tuba in his high school marching band. After entertaining thoughts of a career in medicine, he entered Drake University in Des Moines, Iowa, where he devoted himself to the study of music. He later transferred to Northwestern University, where his teacher was Hermanus Baet.
Milnes' first professional engagement was singing in the Margaret Hillis Chorale in Chicago, followed by a stint in the Santa Fe Opera Chorus, where he accepted opportunities to appear in small roles.
The part of Masetto in Mozart's Don Giovanni provided him with his operatic debut while he was a member of the Boston Opera's touring company in 1960. He then studied briefly with the legendary soprano Rosa Ponselle, who engaged him to sing at the Baltimore Civic Opera (Gérard in Andrea Chénier, 1961). He attracted wide attention as Figaro in Rossini's Il barbiere di Siviglia in 1964, and continued his success with the New York City Opera as Valentin in Gounod's Faust. This led to his first Metropolitan Opera appearance, in the same role in an acclaimed production with Montserrat Caballé in 1965.
His ensuing international career took him to venues in San Francisco, Barcelona, Mexico City, Buenos Aires, Vienna, London, Hamburg, Milan and Chicago, but it was his long association with the Metropolitan Opera, plus his many recordings, that earned him the lion's share of his fame.
Milnes was the continuation of a long line of American baritones, including Lawrence Tibbett, Leonard Warren, and Robert Merrill. He was especially valued for his Verdi roles, and sang all that composer's important baritone parts. He was a striking Escamillo in Carmen, and a powerful Rigoletto. His portrayal of Puccini's Scarpia was notable for overlaying the villain's evil nature with a surface of seductive oiliness--a feat he also managed as Iago in Verdi's Otello.
Milnes' career underwent a decline in the 1980s, but he has continued to appear on a limited basis, and he has remained active as a teacher. ~ All Music Guide, Rovi