Kelly was nominated for the job during a conference call with the 30 player reps Oct. 15 but required a majority vote from the reps in a secret ballot vote. That vote was completed Tuesday.
The Boston lawyer replaces Ted Saskin, who was fired as executive director last May amid allegations he ordered the spying of NHLPA player emails in the midst of a player uprising against his leadership.
A five-player search committee, which consisted of Eric Lindros, Chris Chelios, Mike Cammalleri, Shawn Horcoff and Robyn Regehr, got help from Chicago search firm Reilly Partners and interviewed a long list of candidates before recommending Kelly.
Kelly was a partner at Kelly, Libby & Hoopes, a Boston law firm that specializes in internal investigations and complex civil and administrative litigation. He previously served as an assistant U.S. attorney for the District of Massachusetts, and was involved in the investigation of former NHLPA leader Alan Eagleson.
Kelly was also Marty McSorley's lawyer when the former NHL defenceman was charged for his assault on former Vancouver Canucks tough guy Donald Brashear.