Andrew Wideman Bey Jr. was born in Newark, New Jersey, on October 28, 1939, the youngest of nine children. His father, a window washer born Andrew Wideman, belonged to the Moorish Science Temple of America and followed its custom of taking Bey as a surname; his mother, Victoria (Johnson) Wideman, raised the family. Bey began playing piano at three, attended Newark Arts High School, where he studied piano with Sanford Gold, and was singing in public as a child. He appeared at the Apollo Theater, sang for Louis Jordan, and worked on the children's television show Startime Kids.

At 17 he formed a vocal trio with his older sisters Salome and Geraldine, Andy and the Bey Sisters, which mixed jazz, gospel and soul. The group spent 16 months touring Europe, and the 1988 documentary Let's Get Lost, about Chet Baker, includes footage of the trio delighting a Parisian audience. In April 1959 they recorded two sides in Paris with trumpeter Kenny Dorham, tenor saxophonist Barney Wilen and drummer Kenny Clarke, with Bey on piano and arranging. Back in the United States the trio made three albums, one for RCA Victor in 1961, produced by Chet Atkins, and two for Prestige, Now! Hear! (recorded in August 1964) and 'Round Midnight (recorded in February 1965), both with guitarist Kenny Burrell and bassist Milt Hinton. They won critical respect but little commercial success and broke up in 1967.

Bey then became a sought-after voice on other leaders' records. In 1968 he sang the title track of Max Roach's Members, Don't Git Weary (Atlantic), and in 1969 he sang on two tracks of Duke Pearson's How Insensitive (Blue Note). In the early 1970s he was a member of alto saxophonist Gary Bartz's NTU Troop, singing on Harlem Bush Music: Taifa and Harlem Bush Music: Uhuru (Milestone, 1971) and singing and playing electric piano on Juju Street Songs (Prestige, 1972) and Follow, the Medicine Man (Prestige, 1973). He also began a roughly twenty-year, on-and-off association with pianist Horace Silver, starting with the Blue Note album That Healin' Feelin' (1970), the first of Silver's United States of Mind sets, on which Bey sang most of the program; his sister Salome joined him on the next two. In 1973 he and Dee Dee Bridgewater were the featured vocalists on bassist Stanley Clarke's Children of Forever, and in 1976 he took part in a production of Adrienne Kennedy's play A Rat's Mass, directed by pianist Cecil Taylor at La MaMa in Manhattan.

His own first album as a leader, Experience and Judgment (Atlantic, 1974), was produced by William S. Fischer and showed an Indian influence; it opened with his song "Celestial Blues," which the NTU Troop had also recorded. He then drew back from the spotlight. Through the late 1970s and 1980s he kept working as a guest singer, on albums by trombonist Grachan Moncur III (Shadows, 1977), Pharoah Sanders (Heart Is a Melody, 1983) and Silver (Music to Ease Your Disease, 1988), and his next album under his own name was a live set, As Time Goes By, recorded at the B.P. Club in 1991 and issued on the Jazzette label. He also spent about two years in Austria teaching jazz vocalization, and he returned to the United States in 1993 to sing on Silver's It's Got to Be Funky.

His return as a leader came with the producer Herb Jordan, who backed his comeback. Ballads, Blues & Bey, ten standards with Bey singing and playing piano alone, was recorded in New York in May 1995 and released on Evidence in 1996. It was widely praised and brought him far more attention than he had had in decades. Bey was openly gay, and after being diagnosed as HIV-positive in 1994 he kept working. Shades of Bey (Evidence, 1998) added Gary Bartz, Geri Allen, bassist Peter Washington and drummer Victor Lewis, and Tuesdays in Chinatown (N2K Encoded Music, 2001) used a larger band including bassist Ron Carter, Washington, Lewis and trombonist Steve Turre, with Allen arranging the horns. The Jazz Journalists Association named him Jazz Vocalist of the Year in 2003. American Song (Savoy Jazz, 2004), with Allen, saxophonist Frank Wess and guitarist Paul Meyers, earned a Grammy nomination for Best Jazz Vocal Album at the 2005 awards. He followed it with Ain't Necessarily So (Nocturne, 2007, drawn from a 1997 Birdland engagement) and then two voice-and-piano albums for HighNote: The World According to Andy Bey (2013), nominated for Best Jazz Vocal Album at the 2014 Grammy Awards, and Pages from an Imaginary Life (2014), which won the Best Vocal Album award in the 2014 NPR Music Jazz Critics Poll.

Bey lived for many years in the Chelsea neighborhood of Manhattan. He spent his last years at the Actors Fund Home in Englewood, New Jersey, where he passed away on April 26, 2025, at the age of 85. His nephew, the actor and singer Darius de Haas, announced his death. Bey was survived by his sister Geraldine (Bey) de Haas and many nieces and nephews.

Bey sang in a wide baritone with a range often described as four octaves, reaching up into falsetto, and he accompanied himself on piano, so that his best-known records are voice-and-piano programs of standards, ballads and blues. He named Billie Holiday, Billy Eckstine and Sarah Vaughan among his influences, and he knew Vaughan from Newark. His early years in the NTU Troop and on Silver's vocal projects placed him in spiritual, funk-tinged and gospel-rooted jazz, and Experience and Judgment reached toward Indian music, while his later albums mixed standards by Gershwin, Ellington and Strayhorn with outside material such as Nick Drake's "River Man," which he recorded twice. Ballads, Blues & Bey drew the warmest critical response of his career and made him a songbook interpreter first and a session singer second, and John Coltrane was reported to have counted him among his favorite singers.