Marlena Shaw was born Marlina Burgess in New Rochelle, New York, on September 22, 1939, the year given by English Wikipedia; some other sources give 1942. Her uncle, the trumpeter Jimmy Burgess, introduced her to records by Dizzy Gillespie and Miles Davis, to gospel, and to the singer Al Hibbler, whose phrasing became a model for hers. She sang in a church choir, and at about age ten her uncle brought her on stage at Harlem's Apollo Theater, though her mother would not let her go on the road with his band. She studied music at the State Teachers College in Potsdam, New York (now part of the State University of New York at Potsdam), left without finishing, and took the stage name Marlena Shaw.

In 1963 she worked around New England with a trio led by the trumpeter Howard McGhee, and by the mid-1960s she was a regular at Catskills resorts, Playboy Clubs and New York-area rooms. A 1966 engagement at the Chicago Playboy Club led to a contract with Chess Records, whose Cadet subsidiary issued her first single, "Let's Wade in the Water" (November 1966), and then "Mercy, Mercy, Mercy," a vocal version of Joe Zawinul's tune from Cannonball Adderley's hit record. It reached number 58 on the Billboard pop chart and number 33 on the R&B chart in 1967. The label asked for an album, and Out of Different Bags, recorded in October 1967 at Ter Mar Studios in Chicago with the arranger and producer Richard Evans and issued in February 1968, took its title from the mix of blues, jazz and pop standards it covered. Her second Cadet album, The Spice of Life (November 1969), arranged and produced by Evans and Charles Stepney, held two songs that outlived it: her version of Ashford and Simpson's "California Soul," and "Woman of the Ghetto," which she wrote with Evans and Bobby Miller.

Her accountant brought her to the attention of Count Basie, and after an audition in Las Vegas she sang with the band for about four years from 1968, including a European tour. She also toured for a time with Sammy Davis Jr. In 1972 she left the Basie band and signed with Blue Note Records, where she made five albums. The first, Marlena (recorded in New York in August 1972 with the arranger Wade Marcus), mixed Michel Legrand songs with "Save the Children" and "Wipe Away the Evil" by Horace Silver; it was followed by From the Depths of My Soul (1973) and by Marlena Shaw Live at Montreux, taped on July 5, 1973, at the Montreux Jazz Festival with the pianist George Gaffney, the bassist Ed Boyer and the drummer Harold Jones. Her spoken introduction to the nine-minute "Woman of the Ghetto" on that album was later sampled by St Germain (2000), Blue Boy (1996) and Ghostface Killah (2010). Who Is This Bitch, Anyway? (1975), produced by Bernard Ighner and recorded in 1974 with guitarists Larry Carlton and David T. Walker and the drummer Harvey Mason, opens with a spoken skit in which she plays a streetwalker who turns down a customer. AllMusic gave it four and a half stars and called it her best-selling Blue Note record and her creative peak. The fifth Blue Note album, Just a Matter of Time, followed in 1976.

She moved to Columbia in 1977. Sweet Beginnings (1977) included a "Yu-Ma / Go Away Little Boy" medley, and she sang "Don't Ask to Stay Until Tomorrow," the theme of the film Looking for Mr. Goodbar. Acting Up (1978) and the disco-era Take a Bite (1979), which included a remake of "Touch Me in the Morning," followed. In 1982 she recorded Let Me in Your Life for South Bay, whose "Without You in My Life" had moderate success on the US charts, and she sang "Could It Be You" on the Phil Upchurch album Name of the Game (1984). A live album recorded at the Vine St. Bar and Grill in Hollywood, It Is Love (Verve, 1987), with the pianist Buddy Montgomery, was followed by Love Is in Flight (Polydor and Verve, 1988), which she executive-produced.

Two albums for Concord Jazz brought her back to a jazz setting: Dangerous (1996), with the pianist David Hazeltine, the bassist Peter Washington, the drummer Clifford Barbaro and, on three tracks, the tenor saxophonist Chris Potter, and Elemental Soul (1997), with Hazeltine and, on three tracks, Stanley Turrentine. She was one of the guest singers on Benny Carter's two Songbook albums for MusicMasters (1996 and 1997), duetted with Joe Williams on In Good Company (1989), appeared on Jimmy Smith's Sum Serious Blues (1993), and sang with Ray Brown's trio on two Telarc albums in 1998 and 1999. She recorded Live in Tokyo (2002) and Lookin' for Love (2003) for the Japanese label Eighty-Eight's, played the North Sea Jazz Festival in 1999, 2001 and 2007, and was still working about 175 dates a year as late as 2003, mostly in clubs and on the cabaret circuit.

A longtime Las Vegas resident with five children, Shaw passed away on January 19, 2024. Her daughter MarLa Bradshaw announced the death in a video posted on Facebook, and no cause was given. By then "California Soul" had been licensed for television commercials and had become a favorite of British rare-groove collectors, and Blue Note Europe had begun reissuing her catalog in 2014.

Shaw sat between jazz and soul for her whole career, and critics did not always agree on which side she belonged to. Her Blue Note biography calls her a versatile jazz vocalist who blended pop standards with straight-ahead jazz, and compares her to Dinah Washington and Sarah Vaughan; her obituary in The Guardian said she moved from jazz to soul and back again, and listed Billie Holiday, Ella Fitzgerald and Dinah Washington among her influences. Al Hibbler was the singer she named as an influence on her phrasing. The Cadet records, the Columbia dance albums and much of her Blue Note work, Who Is This Bitch, Anyway? above all, leaned to soul and funk, while It Is Love and the two Concord Jazz albums were built largely on standards and ballads. The New York Times critic Stephen Holden praised her skill at slipping semi-improvised spoken commentary into a song so that it became personal testimony, and in 2005 described a voice with the edge of a meat cleaver; a Los Angeles Times critic called her an evergreen performer in jazz even when she was away from the charts. Scott Yanow of AllMusic was less convinced by her Montreux set, finding her note-bending and lyric delivery overplayed and better suited to soul and pop than to jazz. Hip-hop and dance producers have kept her best-known recordings in circulation. The Subgenres listed for her are the jazz ones her work touches; her soul, disco and R&B records fall outside that list.