Beaser was brought up in a non-musical family. His father was a physician and mother was a chemist. He grew up in Newton, Massachusetts where he distinguished himself at a young age as a percussionist, composer and conductor. He made his debut with the Greater Boston Youth Symphony at Jordon Hall when he was 16, conducting the premiere of his own orchestral work, Antigone. He went on to study with Yehudi Wyner and Jacob Druckman at Yale College, graduating summa cum laude, Phi Beta Kappa in 1976, and later received his Master of Music, M.M.A. and Doctor of Musical Arts degrees from the Yale School of Music. He studied conducting with Otto-Werner Mueller and William Steinberg. Other teachers included Toru Takemitsu, Arnold Franchetti, Goffredo Petrassi and Earle Brown. He studied with Betsy Jolas on a fellowship at Tanglewood. In 1977 he became the youngest composer to win the Rome Prize from the American Academy in Rome. Residence in Rome proved a watershed in his development, and he embraced more tonal language, synthesizing a variety of diverse influences from jazz to folk into his writing.
Beaser has received numerous awards and commissions from orchestras such as the New York Philharmonic the Baltimore Symphony and the Chicago Symphony. He was appointed Professor and Chairman of the Composition Department at the Juilliard School in New York in 1993. In 1999, Beaser was co-commissioned by Glimmerglass Opera, the New York City Opera and WNET-TV to compose The Food of Love, with Terrence McNally as librettist, which was performed at both venues, aired on PBS, and was nominated for an Emmy Award in 2000.
From 1978–1990 he served as co-Music Director and Conductor (along with Daniel Asia) of the innovative contemporary chamber ensemble Musical Elements at the 92nd Street Y, bringing premieres of over two-hundred works to Manhattan. From 1988-1993 he was the Meet the Composer/Composer-in-Residence with the American Composers Orchestra at Carnegie Hall, and served as the ACO’s artistic advisor until January 2001, when he assumed the role of Artistic Director. In 2013 he became the Artistic Director Laureate of the ACO. Beaser founded the Whittaker New Music Readings (currently the Underwood New Music Readings) with the ACO in the early 1990s, providing an opportunity for young composers to receive hearings of their orchestral works. Along with Tania Leon, Beaser spearheaded the Sonidos de Los Americas Festival from 1993–99, bringing composers and works from the Americas to Carnegie Hall. He currently serves as trustee for the American Academy in Rome, the MacDowell Colony, and the American Composers Orchestra. He was elected to the membership in the American Academy of Arts and Letters in 2004.
His works are published by Schott Music.
Beaser was one of the first composers to embrace the "New Tonality." Early works such as The Seven Deadly Sins and Variations for flute and piano show his proclivity for dramatic vocal writing as well as continuous variation technique across a broad canvas. Conductors who have championed his work include Leonard Slatkin, David Zinman, and Dennis Russell Davies and José Serebrier. His incorporation of extant folk materials came in the 1980s though his widely performed Mountain Songs nominated for a Grammy Award in 1986, and continues to the present decade with works such as Souvenirs for piccolo and piano/clarinet and piano and Evening Prayer—an orchestral tone poem which incorporates and deconstructs a Hungarian folk tune. His orchestral music draws from a wide and diverse palette, and he has made dramatic vocal works using texts from poets such as Anthony Hecht, Eugenio Montale and Gjertrud Schnackenberg in The Heavenly Feast, which creates 'a striking fusion of literary and musical poetic images'. His Four Dickinson Songs written for Meagan Miller and the Marilyn Horne Foundation is acrobatic in its demands for the soprano/piano duo and opens the recent Americans in Rome compendium on Bridge records performed by Hila Plitmann and Donald Berman. Recent works include Guitar Concerto for Eliot Fisk, his classmate at Yale, which mixes Andalucian flamenco with bluegrass picking techniques, and was premiered by the Albany Symphony, with David Alan Miller conducting, and The End of Knowing, a consortium commission from twenty-seven wind ensembles, for soprano and baritone and wind ensemble on texts by various poets including Seamus Heaney, Joseph Brodsky, Schnackenberg, Theodore Worozbyt and James Joyce.
- "Guitar Concerto" (Linn Records)
- "Notes on a Southern Sky" (Linn Records)
- "Evening Prayer" (Linn Records)
- "Ground O" (Linn Records)
- The Seven Deadly Sins (Phoenix, London/Argo)
- Chorale Variations, and Piano Concerto (Phoenix, London/Argo)
- The Heavenly Feast (Milken Archives)
- Song of the Bells (New World)
- Notes on a Southern Sky (EMI-Electrola)
- Mountain Songs (Musicmasters, Naxos, Koch, Gajo, Siemens, Nimbus, HM Records Venezuela)
- Landscape With Bells (Innova)
- Psalm 119/Psalm 150 (New World, Divine Grandeur)
- Brass Quintet (ABQ, Summit, Capriccio)
- Souvenirs (Albany)
- Variations for flute and piano (Musicmasters, Koch, Albany)
- Four Dickinson Songs (Bridge)
- Shenandoah (Sonora, Golden Horn)
- Minimal Waltz (Capstone, Guild Music)
- Crutchfield, Will (4 June 1984). "MUSIC: 'HORIZONS '84'". The New York Times. Retrieved 20 March 2017.
- "LUKAS FOSS: Songs of Anguish; Elegy for Anne Frank; Lammdeni; Adon Olam; ROBERT BEASER: The Heavenly Feast – (various performers) – Milken Archive Series". audaud.com. Archived from the original on 19 July 2012. Retrieved 24 March 2015.
- "Jose Serebrier – Beaser: Guitar Concerto". linnrecords.com. Retrieved 4 February 2018.
- "Robert Beaser". Milken Archive. Retrieved 4 February 2018.
- "Music Faculty - The Juilliard School". Retrieved 20 March 2017.
- "American Composers Orchestra - Artistic Leaders Biographies". Retrieved 20 March 2017.
- Beaser, Robert (27 November 2012). "The Reconstruction of Rome". Retrieved 20 March 2017.
- Robert Beaser at AllMusic
- Interview with Robert Beaser, January 18, 1991