Diana Jean Krall was born in Nanaimo, British Columbia, on November 16, 1964, the daughter of Adella Krall, an elementary school teacher who sang in a community choir, and Jim Krall, an accountant who played piano at home. The house had records, including Fats Waller and Bing Crosby, and she began piano lessons at four and sat the Royal Conservatory of Music exams. She played in a high school jazz group and was working in local restaurants by fifteen. A scholarship took her to the Berklee College of Music in Boston, where she studied from 1981 to 1983.

The people who shaped her came next. At a jazz camp in Port Townsend, Washington, she met the drummer Jeff Hamilton, who introduced her to the bassist Ray Brown. Brown heard promise in her playing, became an important mentor, and encouraged her to study in Los Angeles. There she studied with the pianist Alan Broadbent and then with Jimmy Rowles, who urged her to take her singing seriously; she had been singing as little as she could. In 1988 she moved to Toronto to study with the multi-instrumentalist Don Thompson, and in 1990 she moved to New York.

Her first album, Stepping Out, was recorded in Los Angeles on October 18 and 19, 1992, with the bassist John Clayton and Hamilton, produced by Jim West and released in 1993 by the Canadian label Justin Time, with liner notes by Brown. It caught the attention of the producer Tommy LiPuma, who made her second album with her. Only Trust Your Heart (GRP, February 14, 1995) was recorded over four days in September 1994 at the Power Station in New York with Brown and Christian McBride sharing the bass chair, Lewis Nash on drums and Stanley Turrentine on tenor saxophone for three tracks. Then came All for You: A Dedication to the Nat King Cole Trio (Impulse!, March 12, 1996), cut in October 1995 as a trio with the guitarist Russell Malone and the bassist Paul Keller, the instrumentation of Nat King Cole's group. It was nominated for a Grammy for Best Jazz Vocal Performance and stayed on the Billboard jazz chart for 70 weeks. Love Scenes (Impulse!, August 26, 1997), with Malone and McBride, went platinum in the United States.

The breakthrough was When I Look in Your Eyes (Verve, June 8, 1999), with Johnny Mandel arranging and conducting seven of its tracks. It earned her the Grammy for Best Jazz Vocal Performance at the ceremony held in 2000 and a nomination for Album of the Year, the first time in 25 years that a jazz album had been nominated in that category. In August 2000 she toured 20 cities with Tony Bennett. The Look of Love (Verve, September 18, 2001) put her at the front of orchestral settings by Claus Ogerman, played by the London Symphony Orchestra on seven tracks and a Los Angeles studio orchestra on three; it was her first number one in Canada, reached No. 9 on the Billboard 200, went platinum, and won the Juno Award for Album of the Year. Her concerts at the Paris Olympia from November 29 to December 2, 2001, became Live in Paris (Verve, October 1, 2002), which won the Grammy for Best Jazz Vocal Album. In 2002 her mother died of multiple myeloma, within months of the deaths of her mentors Ray Brown and Rosemary Clooney.

In December 2003 she married the English singer-songwriter Elvis Costello at Elton John's estate outside London; their twin sons were born in New York on December 6, 2006. Her next album, The Girl in the Other Room (Verve, March 31, 2004), is the only one so far to include her own original songs, written with Costello. The same year she sang "You Don't Know Me" on Ray Charles's Genius Loves Company and recorded a concert at Montreal's Bell Centre, released as Live at the Montreal Jazz Festival. Christmas Songs (2005), with the Clayton/Hamilton Jazz Orchestra, was her first full-length Christmas album and her first studio record with a big band, and From This Moment On (2006) was nominated for the Grammy for Best Jazz Vocal Album. Quiet Nights (March 31, 2009) was a bossa nova record arranged and conducted by Ogerman and produced by Krall and LiPuma. The same year she produced Barbra Streisand's Love Is the Answer and played piano on five of its tracks, and in 2012 she played piano and arranged the rhythm parts on all but one song of Paul McCartney's Kisses on the Bottom.

The records of her middle period moved further from the standards. Glad Rag Doll (October 2, 2012), produced by T Bone Burnett, took songs of the 1920s and 1930s from her father's 78 rpm collection and gave them a rootsy band with the guitarist Marc Ribot. Wallflower (February 3, 2015), produced by David Foster, was a pop album: two Eagles songs, "Sorry Seems to Be the Hardest Word" by Elton John and Bernie Taupin, 10cc's "I'm Not in Love," Neil Finn's "Don't Dream It's Over," and a duet with Michael Bublé on Gilbert O'Sullivan's "Alone Again (Naturally)." Turn Up the Quiet (May 5, 2017), her return to a standards program with LiPuma producing, won the Juno Award for Vocal Jazz Album of the Year in 2018; LiPuma, who produced it with her, died in 2017. She and Bennett recorded the Gershwin duet album Love Is Here to Stay with the Bill Charlap Trio (Verve and Columbia, September 14, 2018), which received two Grammy nominations. Bennett passed away on July 21, 2023. This Dream of You (September 25, 2020) was chosen from more than 30 unused recordings she had made with LiPuma in 2016 and 2017, and Krall finished it in May 2020.

She remains an active performer. Her 2024 tour band included the bassist Sebastian Steinberg and the drummer Matt Chamberlain, and in 2026 she played a U.S. tour that began January 18 in Jacksonville, Florida. On March 28, 2026, at the Cabot in Beverly, Massachusetts, she performed as a duo with John Clayton. That same month she spent three days with the bassist Ron Carter, playing together for the first time, and a film of the sessions, Ron and Diana - Together, is sold through Carter's website. This Dream of You is her most recent studio album. She is an Officer of the Order of Canada (2005) and a member of the Order of British Columbia (2000), was inducted into Canada's Walk of Fame in 2004, and has sold more than 15 million albums worldwide.

Krall is a contralto and a working pianist, and the combination is what defines her records: she accompanies herself, arranges the trio or small group, and sings in a low, unhurried contralto. Her piano roots run through the swing and stride of her father's records, the Nat King Cole Trio format she adopted on All for You, and the mentoring of Ray Brown and the teaching of Jimmy Rowles, who is also the reason she sings. On the records with Johnny Mandel, Claus Ogerman and Alan Broadbent she is the featured voice in front of a large orchestra, in the tradition of the Great American Songbook; on Quiet Nights that tradition shades into the bossa nova of Antonio Carlos Jobim. She takes songs from outside the standards as well, such as "I Love Being Here with You," written by Peggy Lee, or Joni Mitchell's "A Case of You" on Live in Paris.

The pop side of her career is a large one. She has written and recorded with Costello, she has covered Billy Joel, Joni Mitchell, the Eagles and 10cc, she made Wallflower with the pop producer David Foster, and she produced Barbra Streisand. Her standing in the market is that of a standards singer who sells like a pop act: Billboard ranked her the second-greatest jazz artist of the 2000s, and she is the only jazz singer with eight albums debuting at number one on its Jazz Albums chart. Critics and catalogs file her under jazz, traditional pop and smooth jazz at different times, and each claim has evidence behind it: the jazz case rests on her piano, her trio records, her Grammy for Live in Paris and her mentors, and the pop case on her sales, her orchestral ballad albums and the Costello years.