Kate Victoria Tunstall was born in June 1975 in Edinburgh, Scotland, and was adopted 18 days later. She grew up in St Andrews, Fife, attending Lawhead Primary and spent her last year of high school in New England. Her first performances came in the US, on Church Street in Burlington, Vermont, and also at a commune in rural Vermont. Back in Scotland she was part of a band called Red Light Stylus, and throughout her twenties, she played in independent bands including Elia Drew and Tomoko, focussing on songwriting, and also performed with members of the fledgling Fence Collective including work in the Skuobhie Dubh Orchestra with King Creosote (who later supported her UK tour). She also lived with Gordon Anderson (The Beta Band and The Aliens), whom the song “Funnyman” (on the album “Drastic Fantastic) is about. She goes by KT as her first name, and has explained "[Kate] just makes me think of a buxom lass baking bread for her man working in the fields. I have no problem with that, but it's just not really how I pictured being a rock star." It also differentiates her from fellow singer Katie Melua.

Her own debut album, “Eye to the Telescope”, was released in late 2004, and appeared on “Later… with Jools Holland”, performing "Black Horse and the Cherry Tree", and achieving success by topping the post-show poll on the website for that episode. “Eye to the Telescope” was re-released, peaked at number 3 on the UK charts (it had entered at number 73 on its first release), and was nominated for the 2005 Mercury Music Prize. It was released in the US in February 2006, with “Black Horse and the Cherry Tree” at number 79 on the Billboard Charts, however American Idol contestant Katharine McPhee contacted Tunstall and her asked to use "Black Horse and the Cherry Tree" as her choice for a Billboard-themed week on the show. Tunstall agreed and the song immediately rose to number 23 in the week following McPhee's performance. Tunstall received 3 BRIT award nominations in January 2006 (“Best British Live Act”, “British Breakthrough Act” and “British Female Solo Artist”), and won “Best British Female Solo Artist” (commenting that she wished to share it with fellow nominee Kate Bush). In the same month, she won a European Border Breakers Award (which awards the top-selling EU artists, discounting sales in their home state (in her case, the UK), and later in 2006 she won the Ivor Novello Best Song Musically and Lyrically (for "Suddenly I See").

Tunstall released a new acoustic album in May 2006, “KT Tunstall's Acoustic Extravaganza”, initially only available via mail order from her website, but it was re-released in stores worldwide in October 2006. She received a 2007 Grammy nomination for “Best Female Pop Vocal Performance” (for "Black Horse and the Cherry Tree"), and third album, “Drastic Fantastic”, released in September 2007, reached number 1 on the Scottish Album Charts, number 3 on the UK Charts, and number 9 on the US Charts.

KT Tunstall appears on the Sophie Solomon song "Lazarus" (from the album “Poison Sweet Madeira”), and provided guest vocals for 3 tracks, "Ladino Song", "Refugee" and "Yesterday's Mistake" on the Oi Va Voi album “Laughter Through Tears” (2003). She has also performed "Get Ur Freak On" by Missy Elliott, "My Doorbell" by The White Stripes, and "The Prayer" by Bloc Party. She appears in “Wave”, Japanese singer Yuki’s 2006 album, where she wrote "Yume Miteitai" and "Birthday". She also provided backing vocals for the Travis song 'Under The Moonlight' (from their 2007 album “The Boy With No Name”) and recorded lead vocals for the Leo Abrahams song “City Machine”. "Suddenly I See" was used in the opening scene of the 2006 satirical fashion film “The Devil Wears Prada”.