Stacey Kent was born on March 27, 1965, in South Orange, New Jersey, and grew up between New York and New Jersey. Her paternal grandfather had grown up in France, and she has said he taught her French and read her Baudelaire; her mother taught literature. She has also said she discovered bossa nova at fourteen through the album Getz/Gilberto, made by Stan Getz and João Gilberto. She studied comparative literature at Sarah Lawrence College, spent eight summers in the language programs at Middlebury College (Italian, German, Portuguese and French), and began work toward a master's degree before going to Germany to improve her German. A visit to friends in England in the early 1990s led her to audition for the Guildhall School of Music and Drama in London, which she saw as a way to keep studying without committing to a music career. There she met the saxophonist Jim Tomlinson, and the two were married on August 9, 1991. She stayed in England.

She began singing professionally at Café Bohème in Soho, and after two or three years she was opening for established acts at Ronnie Scott's Club. A demo recording was played on Humphrey Lyttelton's BBC Radio 2 program, and in 1995 she sang "The Passionate Shepherd to His Love" in the Grand Ball scene of Richard Loncraine's film Richard III. Candid Records signed her in 1996. Her debut, Close Your Eyes (1997), was produced by Elliot Meadow, with Alan Bates as executive producer and Tomlinson on tenor saxophone, and she presented it at Birdland in New York that September. Five more Candid albums followed: Love Is... The Tender Trap (1998), Let Yourself Go: Celebrating Fred Astaire (1999), Dreamsville (2000), In Love Again: The Music of Richard Rodgers (2002) and The Boy Next Door (2003), a set built from songs of male singers she admired. She won a British Jazz Award in 2001 and the BBC Jazz Award for best vocalist in 2002, and in those years she also presented jazz programs on BBC radio.

The novelist Kazuo Ishiguro had named her recording of "They Can't Take That Away from Me" among his Desert Island Discs, and he wrote the liner notes for In Love Again. In 2006 he and Tomlinson began writing songs for her; their "The Ice Hotel" won first prize in the jazz category of the International Songwriting Competition. The Lyric, a Tomlinson album on Token that featured her, was named album of the year at the 2006 BBC Jazz Awards. The Boy Next Door reached gold status in France in September 2006, and her first album for Blue Note, Breakfast on the Morning Tram (2007), produced by Tomlinson and containing four Tomlinson and Ishiguro songs, went platinum in France and double gold in Germany; it earned a Grammy nomination for best jazz vocal album at the 2009 ceremony. That year the French minister of culture made her a Chevalier of the Order of Arts and Letters.

Raconte-moi... (2010), her first album recorded in French, drew on French songwriters along with American standards and bossa nova, and reached gold status in France and Germany. Dreamer in Concert was recorded in May 2011 at La Cigale in Paris. The Changing Lights (2013) was a bossa nova-leaning set recorded in Sussex in November 2012 and April 2013, with the Brazilian guitarist Roberto Menescal guesting; the same year she released the live album Ao Vivo with Marcos Valle, marking the 50th anniversary of his career. She moved to Sony in 2014 and made Tenderly (2015), an album of standards with Menescal inspired by his admiration for the Julie London and Barney Kessel records, and in 2017 I Know I Dream: The Orchestral Sessions, her first album with an orchestra, with 58 musicians and arrangements by Tommy Laurence; it won the Jazz Japan Award for best vocal album in 2018. In 2020 and 2021 she released a run of singles and EPs, several with her pianist Art Hirahara, and gathered much of that work on Songs from Other Places (2021), which took best vocal performance at the Jazz Music Awards in Atlanta in 2022.

Summer Me, Winter Me (November 2023) grew out of song requests from listeners, many for songs she had never put on an album, and includes English and French versions of "If You Go Away." In 2023 she received the Prix Ella Fitzgerald at the Montreal International Jazz Festival. In March 2024 Faber & Faber published The Summer We Crossed Europe in the Rain, a collection of sixteen Ishiguro lyrics written for her, and her newest album, A Time for Love, came out on Naïve on April 3, 2026, again with Tomlinson and Hirahara. She has sold more than two million albums worldwide. She has lived in England since the early 1990s, and in a 2014 interview she and Tomlinson described a home in the Colorado Rockies.

Kent sings in her natural, unoperatic voice, which she has said suits bossa nova, and she favors minimalist arrangements and the space between notes; her records are built around Tomlinson's saxophone and flute and, in recent years, Hirahara's piano. On WBGO in 2024 she described her approach as being all about the story, and the host Janis Siegel praised how she conveys feeling without heavy melisma. In a 2001 interview she placed herself closer to the story-first tradition of Rosemary Clooney than to the virtuosity of Mel Tormé, and she named folk and singer-songwriter models, among them Carole King and James Taylor, as close to her as Ella Fitzgerald. Her Brazilian heroes include João Gilberto, Elis Regina and Edu Lobo, and the bossa nova repertoire of Antonio Carlos Jobim runs through The Changing Lights and Tenderly. Her French repertoire goes back to her grandfather, and her original songs pair Tomlinson's music with Ishiguro's deliberately oblique first-person lyrics. She has built large audiences in France, Germany and Britain, and a 2026 review of A Time for Love noted how far her sound has moved toward minimalism in recent years.