He is the eldest son of Val and John Bartlett. His father was in the British Army and the family were re-located around the world a number of times. Kevin attended many schools, including Castle Dyke in Kirkudbright (Scotland), Granville in Celle (Germany), St Peters in Salisbury (England), Hilsea College in Basingstoke (England), St Edmunds in Canterbury (England), Sullivan Upper in Hollywood (Northern Ireland), Uckfield Comprehensive in Sussex (England), and Prince Ruperts in Rinteln (Germany).

When he was 11 years old his mother re-married and he adopted the surname Sheldrake. From the age of 14 he had a strong interest in sports, mainly athletics, but sometimes badminton. He competed in athletic competitions at County and National level, as well as with clubs in Germany. After school he went into Engineering Records in the Royal Air Force, and then moved to the Pay Corps in the British Army.

In 1979, when he reached 18, he left home he took up a civilian job as an accounts clerk/book-keeper for a firm of accountants in Winchester. He then moved around the country stopping in Eastleigh, Southhampton, and Bournemouth before arriving in London at the age of 19. During the day he had varied work including recruitment consultancy and software sales. In the evenings he took up podium dancing at the clubs Heaven, Bang, and Embassy. He won many competitions such as Hot X Buns at Heaven, Limbo Dancing at Bang, and Mister Cover Guy. He appeared on Nicky Hornes Sunday Supplement alongside the olympic ice skater Robin Cousins.

In November 2001 he began treatment with combination therapy which proved successful and he was able to return to mainstream employment. He took up work in the charity sector with Disadvantaged and Disabled People.

He has made television appearances on The Word, Top of the Pops, Big Breakfast, GayTime TV, Eastenders, Call Me Mister, Hope & Glory, Many Splintered Thing, Metrosexuality, Like It Is, and Crime Time. In 1994 he was discovered by Ian Gordon and asked to be the lead singer of Atlas, the Australian pop group. This led to appearances at the main stage of Pride 94 and Winter Pride 94, and a recording contract with BMG/Ariola Australia who flew him to Sidney to record tracks. He has recorded and released a promo CD with Rhythm Shop Records as pop group Upfront. He has co-written lyrics for So High, and has also had lyrics written for him by Rikki Beadle-Blair.

He changed his name to Marques by deedpoll to distance himself from his stepfather but also to make a new start as a recording artist. Throughout his teenage years he competed in athletic competitions with clubs in Germany. In the 1990 Gay Games in Vancouver he won gold and silver medals for athletics. Sheldrake has been involved with the British Lesbian and Gay Sports Federation, and coaching athletics.