His voice is a high dramatic baritone, combining good legato with an incisive rhythmic style; furthermore, he has a commanding and handsome stage presence. By 1965 he had made his debut at the Metropolitan Opera. His international debuts followed soon thereafter, and Milnes became one of the world's prominent Verdi baritones of the 1970s and 1980s.
Milnes was born in Downers Grove, Illinois to a dairy farmer and his wife. As a child, he exhibited strong and varied musical talents. In addition to singing, he also played piano, violin, viola, double bass, clarinet, and tuba. Although his interests did not always lean toward opera, he spent many hours singing to his father's cows and was once found on a tractor practicing an operatic laugh.
While in high school, Milnes planned to be an anesthesiologist, but later returned to music, studying music education at Drake University and Northwestern University, with the idea of becoming a teacher. He attended North Central College before transferring to Drake University and Northwestern University. Milnes was awarded an honorary doctorate from North Central College in 2006. After graduating from Drake, he spent a summer as an apprentice at the Santa Fe Opera and thereafter dedicated himself to becoming an opera singer, studying briefly with the famed soprano Rosa Ponselle.
In 1964, Milnes also made his European debut singing Figaro from The Barber of Seville at the Teatro Nuovo in Milan. However, it was his performance as Miller in Verdi's Luisa Miller in 1968 which catapulted him into international fame.
In the early 1980s, Milnes experienced serious vocal health problems, but he eventually surmounted them. In 1984 he sang in the world premiere of Act I of Sergei Rachmaninoff's opera Monna Vanna, which had been left in piano score by the composer and orchestrated by Igor Buketoff.
In September 1996 Milnes was honored by the French government with the distinguished Chevalier de l'Ordre des Arts et des Lettres. He made his final performance at the Met on March 22, 1997 in Aida. In 1998, Milnes published a memoir, American Aria.
Starting in 2001, Milnes has been bringing his experience and expertise to young rising operatic talent through V.O.I.C.E. (Vocal and Operatic Intensive Creative Experience), which he founded in 2001 with his third wife, Maria Zouves. Their workshops allow educators and performers to share their knowledge through master classes, private coachings, presentations, one-on-one consultations, lectures, and performances. They strive to create a realistic view of the many challenges that singers face throughout their career. The auditor program allows both opera lovers and singers a unique interaction in the creative process.