Gordy was drafted in the second round of the 1957 NFL Draft by the Lions. The 1957 Lions, quarterbacked primarily by Tobin Rote and with Gordy playing a key role in the blocking schemes, won the NFL championship, the last Lions team to do so (as of 2018). He played in three Pro Bowls during his professional career.
Gordy served as president and executive director of the professional football players union, the National Football League Players Association. As such, he was a key negotiator of the first collective bargaining agreement in major professional sports. Shortly after its ratification, he was forced to retire from the NFL due to a lingering knee injury.
"Participatory journalist" George Plimpton stated that Gordy was the inspiration for his second book (of three) about professional American football, Mad Ducks and Bears. Plimpton initially met Gordy in 1960 while doing early research for what would become his first pro football book, Paper Lion, and was told by Gordy that in his opinion there was an obvious wide market for a book about football line play, consisting of young men and boys currently playing those positions and older men who had done so in the past, together forming a potential readership of millions. Gordy, whose football nickname was "Bear" due to his histruteness, was able to interest his erstwhile training camp roommate, Alex Karras ("Mad Duck") in the project as well, although the book was not published until 13 years after this initial meeting. Rather than being the technical work about methods and techniques that Gordy had originally envisioned, it is instead primarily a collection of humorous anecdotes.
Gordy became the California state director of Fellowship of Christian Athletes in 1999. At that time, there were only a handful of public high schools that were participating with FCA. By the time John died, nearly every single high school in Southern California had an FCA group on their campus. Gordy considered this his greatest accomplishment.