Mellor attended Bowmanville High School and then earned a Bachelor of Arts degree in history and Doctorate of Philosophy in the interdisciplinary study of homicide and sex crime from Concordia University, in 2009 and 2019, respectively.

Mellor's first book, Cold North Killers: Canadian Serial Murder, was released on March 3, 2012, by Dundurn Press.

The true crime work documents and analyzes the phenomenon of serial homicide in Canada, providing over 60 cases as examples.

His chapters "Wider Shades of Pale" and "Mincing Words" examine flaws in the current definition of necrophilia and argue for an expansion of the concept to include acts of sexually motivated post-mortem mutilation, posing, and "trophy-taking", as well as certain types of cannibalism and vampirism.

[4] Mellor was editor-in-chief of the e-magazine Serial Killer Quarterly to which he regularly contributed articles, along with fellow true crime writers Harold Schechter, Peter Vronsky, Katherine Ramsland, Michael Newton, Cathy Scott, Burl Barer, Carol Anne Davis, and Robert Hoshowsky.