Although he did not win the competition, he received a contract to record with Syco Music, a label owned by the Britain's Got Talent judge Simon Cowell.
While some journalists have argued Britain's Got Talent producers took advantage of Johnston's background, others have hailed his story as inspirational.
[3] He was given the extensive name Andrew Aaron Lewis Patrick Brannock John Grieve Michael Robert Oscar Schmidt Johnston.
[4] Johnston's parents separated when he was eight months old, and from that time he lived with his mother and three older siblings in Carlisle, Cumbria, in the north of England, where he attended Trinity School.
[3] Johnston's mother, who had no previous association with the cathedral, described her feelings of being overwhelmed by emotion at having her boy singing in such a "stunning building among those extraordinary voices".
[3] Johnston, who attended Trinity School, was subject to abuse and threats from bullies which drove him to contemplate quitting the choir, but he was helped through the ordeal by his choirmaster and the dean and canons of the cathedral.
[5][6] In September 2008, after his appearance on Britain's Got Talent but before the release of his first album, Johnston embarked on a tour of Norway with the choir, performing at Stavanger Cathedral and Utstein Abbey, among other places.
[7] Johnston features as head chorister on one of the choir's albums, The Choral Music of F.W Wadely, released in November 2008.
[12][13] After signing with Syco, Johnston made public appearances, including performing at Andrew Lloyd Webber's birthday celebrations on 14 September,[18] and at Carlisle United's Brunton Park.
[27] After the album's release, Johnston became involved in the Sing Up campaign, appearing in schools around the country to encourage other young people to join choirs.
[21] In December 2008, Johnston made a guest appearance at Whitehaven's Christmas fair,[28] and performed at a carol service in Bradford.
[31][35][36] While a student, Johnston's singing was adversely affected by a broken nose, the result of an unprovoked attack in a Carlisle nightclub on New Year's Day, 2014.
[30] His mother, Morag Brannock, worked for the Office for National Statistics before giving up her job to support her son's career.
[3][21] Prior to his Britain's Got Talent appearances, he attended Trinity School, and later received tuition from a personal tutor.
[21] Johnston said that he "had a lot of support from local people when ... taking part in Britain's Got Talent",[30] and was given a civic award for outstanding achievement by Carlisle City Council in March 2009.
[33] The Carlisle newspaper News and Star reported in September 2012 that Johnston had become the youngest person in the world to be granted a licence to teach the sport.