McGinniss attended Archbishop Stepinac High School in White Plains and graduated in 1964 from the College of the Holy Cross in Worcester, Massachusetts. After his application to the Columbia University Graduate School of Journalism was rejected, something he later pointed to with pride, he became a general assignment reporter at the "Worcester Telegram". He left within a year to become a sportswriter for the "Philadelphia Bulletin" before joining "The Philadelphia Inquirer" as a general interest columnist. In 1979, he became a writer-in-residence at the "Los Angeles Herald Examiner".