Born on October 24, 1959 in New York.
Prior to joining DC Comics, DiDio worked in television, beginning with the American television network CBS in 1981. In 1985 he moved on to Capital Cities/ABC, where he was Public Relations Manager for the network's New York-based daytime soap operas and later worked in the network's Los Angeles offices as Executive Director of Children's Programming.
DiDio came to Mainframe in 1996 after two years at ABC Children's Television as executive director responsible for Saturday morning and after school specials. At the time, Mainframe Entertainment was specifically working on ReBoot and War Planets. He was story editor on Mainframe's first production, the award-winning series 'ReBoot'. Joining the company full-time he became Mainframe's Senior Vice President of Creative Affairs. He was based at the company's Los Angeles business development offices, there DiDio oversaw all development, distribution, marketing and promotion as well as merchandising and licensing of Mainframe's properties. Dan was given the opportunity to pursue other ventures but only after selling Mainframe Entertainment's property Scary Godmother to YTV for one Canadian dollar.
Since 2006, DiDio has been writing a weekly column called "DC Nation" which has then been appearing on the end page of most of DC Comics's main superhero titles; originally, the column was tied in to the yearlong weekly maxi-series 52, a project which he oversaw, but it has continued since.
He was the Senior Vice President — Executive Editor, DC Universe, for DC Comics, having been promoted to that position in October 2004 after having joined the company in January 2002 as DC Universe Vice President — Editorial. However, in February 2020, he departed the company, and it's unclear if he left voluntarily or was fired.
Wizard magazine recognized him as its first ever "Man of the Year" in 2003 for his work on the DC Universe line.