He was born in West Chester, Pennsylvania and began to compose at the age of seven. He studied at the Curtis Institute of Music in Philadelphia before becoming a fellow of the American Academy in Rome in 1935. The following year he wrote his String Quartet in B minor, the second movement of which he would arrange, at Arturo Toscanini's suggestion, for string orchestra as Adagio for Strings, and again for mixed chorus as Agnus Dei.

He tended to avoid the experimentalism of some other American composers of his generation, preferring relatively traditional harmonies and forms until late in his life. Most of his work is lushly melodic and has often been described as neo-romantic, though some of his later works, notably the Third Essay and the Dance of Vengeance, display a masterful use of percussive effects, modernism, and neo-Stravinskian effects.

His songs, accompanied by piano or orchestra, are among the most popular 20th century songs in the classical repertoire. They include a setting of Matthew Arnold's Dover Beach, originally written for string quartet and baritone, the Hermit Songs on anonymous Irish texts of the 8th to 13th centuries, and Knoxville: Summer of 1915, written for the soprano Eleanor Steber and based on an autobiographical text by James Agee, the introductory portion of his novel A Death in the Family. Barber possessed a good baritone voice and, for a while, considered becoming a professional singer. He did make a few recordings, including his own Dover Beach.

Barber's Piano Sonata, Op.26 (1949), a piece commissioned by Richard Rodgers and Irving Berlin, was first performed by Vladimir Horowitz. It was the first large-scale American piano work to be premiered by such an internationally renowned pianist.

Barber also composed several operas. Vanessa, composed to a libretto by Gian Carlo Menotti (his partner both professionally and in their personal lives), premiered at the Metropolitan Opera in New York City. It was a critical and popular success, and Barber won a Pulitzer Prize for it. At the European premiere it met with a chillier reception, however, and is now little played there, although it remains popular in America.

Barber produced three concertos for solo instruments and orchestra, one for violin, one for cello, and one for piano. The Piano Concerto was composed for and premiered by pianist John Browning, on September 24, 1962, with Erich Leinsdorf and the Boston Symphony Orchestra at Lincoln Center, New York. The New York Philharmonic commissioned an oboe concerto, but Barber managed to complete only the slow, central, Canzonetta before his death.

Among his purely orchestral works, there are two Symphonies (1936; 1944), the Overture The School for Scandal (1932), three Essays for orchestra (1938; 1942; 1978) and the late Fadograph on a Yestern Scene (1973). There are also large-scale choral works, including the Prayers of Kierkegaard (1954) and The Lovers (1971). Prayers of Kierkegaard is based upon the writings of the Danish existential theologian Søren Kierkegaard.

In addition to the Sonata, his piano works include Excursions Op. 20, Three Sketches, Souvenirs, and various other single pieces.

Although never a prolific composer, Barber wrote much less after the failure of his opera Antony and Cleopatra. This had a libretto by film and opera director Franco Zeffirelli, and had been commissioned to open the new Metropolitan Opera House at Lincoln Center for the Performing Arts in 1966. The opera was more favorably received in 1975, presented in the intimate setting of the Juilliard School with the partnership and stage direction of Gian Carlo Menotti, and was subsequently recorded.

Samuel Barber died in New York City in 1981.