Eva Marie Cassidy was born on February 2, 1963, in Washington, D.C., the third of four children of Hugh Cassidy, a teacher, sculptor and musician, and Barbara Cassidy, a horticulturist from Bad Kreuznach, Germany. She grew up in Oxon Hill and then Bowie, Maryland. Her father started teaching her guitar when she was nine, and she played in a family folk act with him and her brother Dan, a fiddler. At eleven she was singing and playing with a Washington-area band called Easy Street, and at Bowie High School, where she graduated in 1981, she sang with a band called Stonehenge. In the summer of 1983 she sang and played six days a week at the Wild World amusement park. Music never paid the bills for long. She took art classes at Prince George's Community College, worked off and on as a plant propagator at a nursery from 1981 to 1995, and in her last year painted murals in elementary schools.

In 1986 a high school friend, David Lourim, asked her to sing on a recording by his band Method Actor. The session was at Black Pond Studios, where she met the engineer and bassist Chris Biondo. Biondo found her session work, and over the next few years she sang backup for the go-go band E.U. and the rapper E-40. In 1990 the two of them formed the Eva Cassidy Band with the guitarist Keith Grimes and a rotating cast of drummers, among them Raice McLeod, with the pianist Lenny Williams joining for bigger rooms and studio dates. They played Washington clubs, covering far more ground than a club band usually does.

In 1992 Biondo played a tape of Cassidy for Chuck Brown, the bandleader known as the Godfather of Go-Go, who had wanted to record an album of jazz and blues standards. The result was The Other Side, released that year by Liaison Records and credited to Chuck Brown and Eva Cassidy. It mixed duets with solos and ran from "Fever," "Gee, Baby, Ain't I Good to You" and "Red Top" to "You Don't Know What Love Is" and "The Shadow of Your Smile." Cassidy sang "God Bless the Child," "The Dark End of the Street" and "Over the Rainbow" alone. The bassist Keter Betts, long associated with Ella Fitzgerald, was among the players. Brown's following got the band into the better local rooms, including Blues Alley, the Birchmere, Wolf Trap and the Kennedy Center.

Record labels came to listen and then passed. Her demos covered folk, jazz, blues, gospel, R&B and pop, and nobody could say how to market a singer who would not pick one. She won five Washington Area Music Association awards, known as Wammies, in the three years before 1996, in categories that included jazz traditional vocalist, jazz contemporary vocalist and roots rock and traditional R&B vocalist. In 1994 Blue Note Records paired her with the Philadelphia group Pieces of a Dream. She sang on two tracks of their 1995 album Goodbye Manhattan and toured with them that summer, but the pop-jazz setting did not suit her and she went back to her own gigs.

In January 1996 she recorded two nights at Blues Alley, the Georgetown jazz supper club founded in 1965. A technical fault ruined the first night's tape, so the album came entirely from the second, Wednesday, January 3. She was fighting a cold and was unhappy with how she sounded, and agreed to release Live at Blues Alley only after a studio take of "Oh, Had I a Golden Thread," Pete Seeger's song and her favorite, was added. It came out in May 1996, funded by Cassidy and her circle, and Washington reviewers liked it. A friend, Bryan McCulley, had filmed part of the second set on a camcorder.

That summer a hip that ached after days on a stepladder turned out to be broken. A malignant mole had been removed from her back in 1993, and the cancer had spread to her bones and lungs. On September 17, 1996, friends and family filled The Bayou for a benefit concert for her, and she closed it with "What a Wonderful World," her last public performance. Eva Cassidy passed away on November 2, 1996, at her family's home in Bowie, Maryland. She was 33.

Her music reached most listeners after that. Biondo finished the studio album she had been making, Eva by Heart, released in 1997. Blix Street Records, whose head, Bill Straw, had been sent a copy of Live at Blues Alley by the singer Grace Griffith, issued the compilation Songbird on May 19, 1998. It was little noticed for about two years. Then, in 2000, the BBC Radio 2 presenters Mike Harding and Terry Wogan played "Fields of Gold" and "Over the Rainbow," the response was overwhelming, and McCulley's camcorder clip of "Over the Rainbow" was shown on Top of the Pops 2 before Christmas. Songbird went to No. 1 on the UK Albums Chart, finished 2001 as the eighth best-selling album of the year in Britain and has been certified six times platinum there. Imagine (2002) and American Tune (2003) also reached No. 1 in the UK, and in 2007 the singer Katie Melua recorded a new vocal over Cassidy's "What a Wonderful World" for a British Red Cross charity single that topped the UK singles chart. Later releases include Somewhere (2008), Simply Eva (2011), the full 31-song Nightbird from the Blues Alley recordings (2015), I Can Only Be Me (2023), on which her original vocals were set against new orchestral arrangements played by the London Symphony Orchestra, and Walkin' After Midnight (2024), a recording of a November 1995 gig at the King of France Tavern in Annapolis. The documentary The Essence of Eva premiered at the 2025 Galway Film Fleadh. A jazz-themed collection, Jazzed, pairing her vocals with four new band arrangements by Christopher Willis and two of the orchestral settings from I Can Only Be Me, is due from Blix Street on November 13, 2026.

Cassidy sang with a clear, powerful soprano, steady pitch and little ornament, and she accompanied herself on acoustic guitar. What set her apart was range of material and the way she made each song sound like hers. The Washington Post wrote, around the release of Live at Blues Alley, that she could sing folk, blues, pop, jazz, R&B or gospel and make whatever it was sound like the only music that mattered. A fact sheet kept by her cousin names Ella Fitzgerald, Sarah Vaughan, Louis Armstrong and Ray Charles among her influences, alongside Joan Baez, Stevie Wonder, Pete Seeger, Joni Mitchell, Bonnie Raitt and Buffy Sainte-Marie.

Her jazz credentials are real, and so is the fact that most of her catalogue is not jazz. The jazz side is the repertoire and the rooms: "Autumn Leaves," "Cheek to Cheek," "Honeysuckle Rose," "Blue Skies," "You've Changed," "Blues in the Night," "At Last" and Duke Ellington's "It Don't Mean a Thing" appear in her sets and on her records, and her best-known live album was cut at one of Washington's best-known jazz clubs. Billie Holiday's "God Bless the Child" is on The Other Side and her "Fine and Mellow" is on Live at Blues Alley. Her Wammies were for jazz vocals as well as for R&B, and the writer Michael Bailey, reviewing Nightbird for All About Jazz, likened her to a modern song stylist in the manner of Frank Sinatra. Around that sits a large body of folk and pop: Sting's "Fields of Gold," Paul Simon's "Kathy's Song" and "American Tune," Cyndi Lauper's "Time After Time," Christine McVie's "Songbird," Stevie Wonder's "I Can Only Be Me," traditional ballads such as "Waly Waly," and the spirituals "Wade in the Water" and "Wayfaring Stranger." AllMusic files her under pop and rock, with the style tags adult alternative and contemporary singer-songwriter, while Wikipedia calls her a singer known for jazz, folk and blues. The two subgenre tags here are the ones that fit best, and neither covers everything she sang.