In 1987 she married an American investment banker, Michael Fortier; the couple divorced in 2000, following revelations of her affair with Stephen Quinn, publisher of Vogue and GQ magazines. In 2001, she married Quinn; during this marriage, she had an affair with David Blunkett, Home Secretary in Tony Blair's ministry. Quinn's three-year affair with David Blunkett ended acrimoniously in mid-2004. The affair was revealed by the News of the World in August 2004, according to the prosecution in the R v Brooks, Coulson and six others trial in October 2013, after the newspaper had intercepted voicemails.

A native of Los Angeles, California, she is one of two daughters of businessman Marvin Solomon and Actress Lugene Sanders. She majored in Victorian Studies at Vassar College. She has written for The Wall Street Journal, Vogue and UK newspapers The Daily Telegraph, The Times, Evening Standard, and The Independent. Before taking her position at The Spectator in 1996, she was the Communications and Marketing Director for Condé Nast Publications in the UK.

During that period Quinn gave birth to one son and became pregnant with a second child. The paternity of the two children became a matter of dispute. DNA tests confirmed Blunkett's paternity of Quinn's elder child. Following the end of the affair between Quinn and Blunkett, moves by him to gain informal access to the first child were rejected by Quinn, and in early December 2004 Blunkett petitioned the Family Division of the High Court to grant him legal access. Controversy around a number of matters arising from the affair, particularly concerns over the handling of the visa of Quinn's nanny, contributed to Blunkett's resignation in mid-December 2004. Shortly after Blunkett's resignation it was revealed by the News of the World that Quinn had also had an affair with Simon Hoggart, a political Journalist and regular contributor to The Spectator.

In February 2005, Quinn gave birth to a second son. A month later, Blunkett announced that DNA tests had revealed he was not the father of Quinn's second child. Stephen Quinn denounced Blunkett's renewed interference in his family's life the following day. On 24 November 2006, Kimberly Quinn resigned from her post at The Spectator.

Since then, she has written a series of time travel adventures for young adults; the Chronicles of the Tempus series. The first work, The Queen Must Die (2010) was followed by The Queen at War (2013).