Alexandria "Sandi" Thom was born in August 1981 in Macduff, Scotland. Whilst attending Robert Gordon's College in Aberdeen, Thom was singing and playing keyboards in a covers band called The Residents. Thom and the band travelled across Scotland, playing in pubs and clubs, but at the age of 17, she moved to Liverpool to attend the Liverpool Institute of Performing Arts (LIPA), where she sang in a gospel choir called Love and Joy, and also formed her own 7 piece band, who entered a BBC Talent urban music competition (produced in association with BBC Radio 1) and made it to the semi-finals. The band also recorded an EP, "Time To Breathe", at Parr Street Studios (the band included Jake Field on keyboards, who went on to co-produce her first 2 albums). Thom graduated from LIPA with a BA (Hons) in Performing Arts in 2003, and moved to London to pursue her songwriting career. She signed to Windswept Pacific Music in 2005, an independent music publishing company with artists on its roster such as Alice Cooper, The Futureheads and Nick Cave. She also signed a record contract with a small record label called Victory Legacy, who released her debut single, "I Wish I Was A Punk Rocker (With Flowers In My Hair)" in late 2005, but the song failed to garner major airplay and the album release was delayed.

Following a series of online webcast concerts, consisting of 21 performances from her basement in Tooting in February and March 2006, "I Wish I Was A Punk Rocker..." was re-released in May 2006 on Sony’s RCA Records UK (Thom having signed with Sony due to the success of her online webcasts). On download sales alone it achieved number 15 on the general charts and number 7 on the official Downloads chart, and on release, climbed to number 2 on both charts. It entered the Irish Singles chart at number 10, climbing to number 1, and it also topped the Australian ARIA charts for 10 weeks, becoming Australia's highest selling single of 2006. Debut album ”Smile…It Confuses People” was released in June 2006, debuting at number 1 on the UK Album chart, selling over 700,000 copies worldwide. It also topped the Irish Album chart, made number 5 in New Zealand, and number 11 in Australia.

In May 2008, Sandi Thom released the single “The Devil’s Beat”, which reached number 58 on the UK Singles chart. It was the first single from her sophomore album “The Pink & The Lily”, which entered the chart at number 25. Second single "Saturday Night" failed to chart on its release.

Sandi Thom has sold over a million albums and a million singles worldwide.