Warren worked briefly as a junior sports reporter on Fleet Street after being expelled from Dulwich College and then completing his education at Reigate Grammar School.
Warren rose to fame as an "open line" radio talk show host, a career he would enjoy for 35 years, the longest such tenure in North America.
In March 2006 he left radio to concentrate on his work as an investigative journalist probing cold cases and wrongful convictions.
[2] An outspoken critic of the Canadian justice system, Warren had in the past used his show to campaign on behalf of wrongfully convicted persons such as David Milgaard, Steven Truscott, James Driskell, Thomas Sophonow and on behalf of the families of victims of alleged serial killer Robert Pickton.
He has donated personal archives to the University of Manitoba judged to be of "outstanding significance and national importance" by the Canadian Cultural Property Board.