Kelly's first introduction to lacrosse was at Boys' Latin School, Baltimore, where he was a member of the 1932 Maryland Scholastic Association champions. The following year Boys' Latin lost the title in the play-off game. Kelly was an All-Maryland Prep selection as goalie.

Loyola College, after an absence from lacrosse circles for approximately ten years, resumed collegiate lacrosse in 1938 and Kelly was named head lacrosse coach. He coached at Loyola until the end of 1941, when he resigned because of World War II. His Greyhounds, who never had a losing season, won sixty-five percent of all their games.

Kelly was named editor of the Lacrosse Coaches Association Newsletter in December 1951. He changed the name of the publication to the Lacrosse Newsletter in 1954 and has continued to edit and publish the Newsletter since that time. In addition to editing the Lacrosse Newsletter, Kelly also promotes lacrosse by encouraging editors of other sports publications to give greater coverage to lacrosse.

His contacts among the college coaches have enabled a number of high school lacrosse players to receive financial help in college, boys who otherwise might have been unable to attend college. His promotion work has also been responsible for at least two colleges recognizing lacrosse as a varsity sport. His advice and assistance to students at the University of Notre Dame in helping to establish lacrosse on a club basis led to the setting up of the Notre Dame John F. Kelly Trophy, which is awarded to the winner of the Notre Dame Invitational Lacrosse Tournament.

Several sports writers consider the Newsletter their lacrosse bible. Jack Kelly served as Chairman of the USILA Publicity Committee from 1954 to 1966. He has been a member of the Board of Directors of the Lacrosse Foundation, Inc., since it was established ten years ago. In 1958 he received the USILA award for his contribution to lacrosse during the year.