Gilmore was born in Oxford to Irish parents and lived in the village of North Aston, Oxfordshire. She became interested in music as a result of her father's record collection, which included work by Bob Dylan, Joni Mitchell, and The Beatles. Later, she listened to Elvis Costello, Tom Waits, and The Replacements, among others. She began writing poetry at the age of 15 to cope with the divorce of her parents.
Gilmore released her first album as a teenager, entitled Burning Dorothy, in 1998 and over the course of the next four years, released increasingly well-received albums that earned her a reputation in the UK music press but no chart success.
In 2002 Gilmore shared lead vocals with Kellie While, beside musicians Maartin Allcock; John Kirkpatrick, Robbie McIntosh, Michael McGoldrick and Simon Swarbrick in the Reel and Soul Association. The project mixed American soul and British Folk music. The group's eponymously titled album gained considerable mainstream attention which resulted in numerous TV and radio appearances including the BBC's Top of the Pops 2.
Gilmore finally made a breakthrough at 23 with the release of Avalanche in August 2003, which became her first album to break into the Official UK Album Chart, at #62, and spawned two minor hit singles, "Juliet (Keep That in Mind)" and "Mainstream", for which she garnered acclaim for producing a low-budget music video filmed in a local Virgin Megastore. The video received exposure on the BBC's flagship music show Top of the Pops 2.
In 2004, folk singer Joan Baez personally invited Gilmore to open for her during her tour leading up to the US presidential election.
In 2005, Gilmore continued touring commitments, for the first time not releasing a new album (the covers collection Loft Music was widely released during 2004). In October 2005, she and Stonier married in a ceremony near their home in Cheshire.
Gilmore finally returned to recording with the release of Harpo's Ghost in August 2006, after a two-and-a-half-year absence of new material. This was her first album on major label Sanctuary Records after many years of independent releases. The album was once again acclaimed in the music press and UK radio lent their support to the single "Cheap Tricks". Gilmore has been touted by Uncut magazine as "the best British singer-songwriter of the last 10 years...and then some" and has gained steady acclaim for each of her albums.
On 14 November 2006, Gilmore gave birth to her first child with Stonier, a son named Egan, having conducted a UK tour in the autumn whilst heavily pregnant.
Subsequent to the release of Harpo's Ghost she parted company with her manager Sara Austin, left Sanctuary Records and released EP The Threads independently on her March 2007 UK tour with remaining copies sold on her website afterwards.
On 19 May 2008 Fruitcake Records (via Fullfill and distributed by Universal Records) released Liejacker, Gilmore's eighth album featuring contributions from Joan Baez, Dave McCabe, and Erin McKeown. It was preceded on 12 May by the single "Old Soul", a duet with McCabe. In June 2008, Gilmore signed to Rykodisc (Warner) for the United States. Liejacker was released in the US on 23 September 2008.
Thea's first live album, Recorded Delivery, was released on 25 May 2009, on Fullfill/Universal. The recordings are taken from UK shows during 2006 and 2008, with the first half of the album being acoustic, and the second half being electric, with a full band. In July 2009 she released a yearly subscription service / fan club, Angels in the Abattoir. Gilmore rounded out 2009 with the release of an album of Christmas- and winter-themed songs, Strange Communion, featuring eight originals penned by Gilmore and/or Stonier as well as two cover versions – Yoko Ono's "Listen, the Snow is Falling" and Elvis Costello's "The St. Stephen's Day Murders."
Beginning in October 2010, Gilmore and her band were engaged in a UK tour and had good reviews.
In January 2011, Gilmore appeared at Glasgow Royal Concert Hall in a tribute concert celebrating the 70th Birthday of Bob Dylan. She performed versions of "I Pity the Poor Immigrant" and "Masters of War." Subsequently, Gilmore entered the studio with producer and husband Stonier and recorded the entire set of tracks found on Dylan's original release of John Wesley Harding. The album – also titled John Wesley Harding – was released 23 May 2011.
2011 saw the release of a collaboration with the late Sandy Denny entitled Don't Stop Singing and, in 2012, the CD single "London" was released from the album (and featured on the BBC coverage of the London 2012 Olympics montage of team GB medal winners). The single was also released as an exclusive Record Store Day 7″ single on 21 April.
In July 2011, Gilmore gave birth to a second son, Asher.
In 2013 Gilmore released a new album of original material Regardless to critical acclaim and much exposure on BBC Radio 2.
In May 2015 Ghosts And Graffiti was released, a retrospective with 4 new songs, and 6 newly recorded versions of songs from her back catalogue
Gilmore will release The Counterweight in June 2017 through Cooking Vinyl Records.Burning Dorothy (1998)
The Lipstick Conspiracies (2000)
Rules For Jokers (2001)
Songs From The Gutter (2002)
Avalanche (2003) UK #62
Loft Music (2004)
Harpo's Ghost (2006) UK #69
Recorded Delivery [live] (2009)
Strange Communion (2009)
Murphy's Heart (2010) UK #70
John Wesley Harding (2011)
Don't Stop Singing with Sandy Denny (2011) UK #89
Regardless (2013) UK #39
Ghosts and Graffiti (2015) UK #39
The Counterweight (2017) UK #40
Instead of the Saints (1998)
As If EP (Limited Edition) (2001)
The Threads EP (Limited Edition) (2007)
Beginners EP (Limited Edition) (2012)
Girl Mercury EP (Limited Edition) (2015)
"Saviours and All" (2001)
"Fever Beats" (2002)
"Juliet (Keep That in Mind)" (2003) UK #35
"Mainstream" (2003) UK #50
"Cheap Tricks" (2006)
"Old Soul" (2008)
"You Spin Me Right Round" (2008)
"That'll Be Christmas" (2009)
"You're The Radio" (2010)
"Teach Me to Be Bad" (2010)
"London" (lyrics by Sandy Denny) (2012) UK #86
"Love Came Looking for Me" (2013)
"Live Out Loud" (2015)
Harpo's Ghost – 3 track acoustic performance (2006)