John Holding was called to the Ontario Bar in 1959, followed by the Bars of Alberta and the Yukon. In 1971, he was appointed a Queen's Counsel.

Mr. Holding was a senior partner with Borden Ladner Gervais LLP and its predecessor, Toronto law firm Borden & Elliot. He retired as a senior partner and former head of litigation in December 2002, after 43 years with the firms. Mr. Holding is a member of the Canadian Bar Association, The Advocates' Society, the Royal Aeronautical Society and the Lawyer-Pilots Bar Association. He has been recognized nationally and internationally as a leader of the Canadian aviation bar.

John Holding is now a member of the mediation and arbitration panels of ADR Chambers, a Toronto-based alternative dispute resolution group.