Diane Joan Schuur was born December 10, 1953, in Tacoma, Washington, two months premature and weighing under three pounds. The high-oxygen incubator treatment standard in neonatal care at the time cost her the sight in both eyes, a condition called retinopathy of prematurity; she has been blind since birth. Her mother, an amateur jazz devotee whose record collection ran heavy on Duke Ellington and Dinah Washington, nicknamed her "Deedle-Babes," which shortened over time into "Deedles," the name Schuur has performed and recorded under ever since. She picked out tunes on the family piano by ear starting at age three and had learned Washington's "What a Difference a Day Makes" while still a toddler. Her mother died of cancer in 1967, when Schuur was 13.

Schuur attended the Washington State School for the Blind in Vancouver, Washington, from ages four to eleven, commuting the roughly 150 miles home some weekends by train on her own, before finishing her education in public schools and later studying voice at the University of Puget Sound. At twelve she was given a recording by the blind pianist George Shearing and taught herself its material by ear; a family-arranged meeting with Shearing during one of his Seattle engagements convinced her a career in music was possible. She made her first paid public appearance at ten, singing at a Tacoma Holiday Inn, and at eighteen was introduced to country singer Jimmy Wakely, who arranged her first recording session, a 1971 single called "Dear Mommy and Daddy."

Her professional breakthrough came in 1975, at 21, when an informal backstage audition for Doc Severinsen at the Seattle Opera House caught the ear of Severinsen's drummer, Ed Shaughnessy, who invited her to sing with him that year at the Monterey Jazz Festival. A high-profile return engagement at Monterey in 1979 put her in front of Stan Getz, who was captivated by her set and became her mentor and most consistent advocate, later comparing her to Sarah Vaughan and Ella Fitzgerald. Getz brought her into an all-star White House performance for the Reagan administration alongside Dizzy Gillespie, Chick Corea, Jon Faddis, and Itzhak Perlman, filmed for PBS; when GRP Records co-founder Larry Rosen caught the broadcast, he signed her immediately. Between 1984 and 1997 Schuur recorded eleven studio albums plus two compilations for GRP.

Her fourth GRP album, Timeless (1986), produced and arranged by Dave Grusin with a guest tenor solo from Getz himself, won Schuur her first Grammy Award, Best Jazz Vocal Performance, Female, at the 29th Annual Grammy Awards in 1987. The follow-up, Diane Schuur and the Count Basie Orchestra (1987), recorded live with the "ghost" Basie band under the direction of tenor saxophonist and arranger Frank Foster, repeated the win a year later at the 30th Annual Grammy Awards, making Schuur the only artist besides Ella Fitzgerald to take the category in back-to-back years. That session doubled as guitarist Freddie Green's final recorded performance; he died a week later. The album topped Billboard's traditional jazz chart for 33 weeks.

Schuur's later GRP catalog kept mixing straight jazz with pop and R&B material: Talkin' 'Bout You (1988), Pure Schuur (1991) and Love Songs (1993), the latter two both earning Grammy nominations for Best Traditional Pop Vocal Album, In Tribute (1992), and Heart to Heart (1994), a full duet album with blues guitarist B.B. King that entered the Billboard jazz chart at Number 1. Friends for Schuur (2000), produced by Phil Ramone, gathered career-spanning guest turns from Ray Charles, Stevie Wonder, and Herbie Hancock, plus an archival feature from Getz. In 1999, Atlantic Records founder Ahmet Ertegun signed Schuur directly, releasing Music Is My Life; the album's booklet reproduces an abstract oil painting Frank Sinatra gave her after she filled in for Liza Minnelli at a 1988 Palm Springs benefit, with Quincy Jones conducting.

Schuur's 2000s work moved through Concord Records, including Swingin' for Schuur (2001) with Maynard Ferguson's big band, Midnight (2003), built around new songs written and produced by Barry Manilow, and Schuur Fire (2005), a Latin-jazz session with the Caribbean Jazz Project and Brazilian guitarist Oscar Castro-Neves. In 2011 she departed from jazz almost entirely for The Gathering, a country album on Vanguard produced by Steve Buckingham that paired her with Alison Krauss, Vince Gill, and Mark Knopfler on individual tracks, a project she has said was inspired partly by thoughts of her pianist father and by Ray Charles's own country crossover. She returned to the Getz/Sinatra songbook that shaped her career on I Remember You (With Love to Stan and Frank) (2014), her debut for Jazzheads, and closed the decade with Running on Faith (2020), co-produced with saxophonist Ernie Watts. Schuur announced her retirement from touring in February 2024, citing the effects of Ménière's disease on her performing stamina.

Schuur sings with a three-and-a-half-octave range and absolute pitch, developed entirely by ear; she never learned to read music conventionally, finding braille notation impractical for live piano performance, and instead accompanies herself onstage from memory whether leading a trio or a full orchestra. Dinah Washington was her formative influence, and Schuur's phrasing carries some of the same blues-inflected directness, but her dynamic range is her signature: a single phrase can leap from a little-girl coo into a full-throated, gospel-tinged wail within a breath. Early reviewers nicknamed her "Lady Overkill" for a tendency to oversing, a habit she has credited Stan Getz with talking her out of, recalling his advice that "less is more." That range made her equally at home in a big-band swing setting with the Count Basie Orchestra, a stripped-down blues duet with B.B. King, or later, a Nashville country session, without abandoning a fundamentally jazz-rooted sense of time and phrasing.