Born in Scotland, Simpson arrived in Australia in 1976. Simpson worked as an investigative Journalist for The Sydney Morning Herald for twelve years.

She has authored and co-authored seven books. Her first book, published in 1989, co-authored with Sandra Harvey was Brothers in Arms about the Milperra massacre. The best-selling book was made into a television mini-series, Bikie Wars: Brothers in Arms produced by Screentime, and screened on Channel 10 in May 2012. The series peaked at 1.43 million viewers and is available on DVD. Her first fiction novel, The Curer of Souls was published in 2006 by Random House. One of her crime books, My Husband My Killer, co-authored with Sandra Harvey was made into a telemovie starring Colin Friels (2000). Her third crime book, co-written with Sandra is about the serial killer John Wayne Glover. Her next book was Honeymoon Dive, co-authored with Jennifer Cooke, and published by Pan MacMillan on September 2010 about the scuba diving death of Tina Watson on the Great Barrier Reef. It was later updated by the authors after Watson's husband Gabe was acquitted in February 2012. Her latest book, launched in August 2014, is 'Where is Daniel"' written with Bruce and Denise Morcombe about the abduction and murder of their son, Daniel.