Maloney was born in London, to Irish parents, and began boxing at school. After attempts to become a Catholic priest, jockey and professionalfootballer, Maloney became a chef but continued to box and began training other boxers and organising amateur contests. By the late 1970s this had led to a career as a professional trainer, working with promoter Frank Warren.
After splitting with Warren in the 1980s, Maloney moved into management and began promoting professional fights, becoming Lennox Lewis's manager in 1989.
While known as the promoter who took Lennox Lewis to the top, Maloney has also guided four other fighters to World Titles and has managed a string of British, European and Commonwealth Champions. In 2009, the 'Boxing Binman', Rendall Munroe, made his fifth successive defence of his European Super Bantamweight title and later thrice fought for a world title, twice on an interim basis, drawing once and losing twice.
On 14 September 2009 Maloney suffered a heart attack while watching John McDermott lose a contentious decision to Tyson Fury; significant heart damage was discovered when Maloney was admitted to hospital with shock after finding the body of boxer friend Darren Sutherland. It was reported that Maloney was not welcome at Sutherland's funeral service, although reports circulated that her wife, Tracey, and mother, Maureen, attended.
Maloney announced the decision to retire from boxing in October 2013.
In April 2015 Maloney announced that, following the completion of her gender reassignment, she will be returning to boxing to promote again.
Maloney was married for over 15 years to second wife Tracey; they have two daughters. Maloney has a daughter from her first marriage and is a supporter of Millwall Football Club. Maloney said in her first televised interview as an open trans woman that she and Tracey are now divorced, but that she has been "very supportive". In 2015, Maloney admitted to nearly having strangled Tracey ten years prior, stating that it was caused by a combination of pent-up frustration, anguish over her gender identity, and alcohol consumption.
In August 2014, Maloney announced publicly that she is now known as Kellie, and is undergoing gender reassignment. Lennox Lewis was initially shocked at the news but expressed respect for Maloney's decision.On a radio interview she discussed her family's reaction with her mother Maureen.
Maloney had already received counselling, hormone therapy, and voice coaching. She had stated that final sex reassignment surgery was set for early 2015. In April 2015, Maloney announced that her gender reassignment was now complete.