O'Brien died from complications of Parkinson's disease, his family said.
O'Brien first met Nicklaus in 1962 when he tried to persuade the new U.S. Open champion to play in the Canadian Open. Ten years later, Nicklaus asked him to work for his company and handle his PGA Tour affairs.
'Larry was side-by-side with me for the majority of my career and served an important role in my company, as well as for my family,' Nicklaus said. 'Larry was a good friend to us, someone we considered one of the family.'
O'Brien covered crime for the Montreal Star and did radio for the Brooklyn Dodgers farm team in Montreal. He moved over to television and called the first sporting event on TV in Canada, a Montreal Royals baseball game on July 25, 1952. He also broadcast the Grey Cup and the Montreal Canadians.
He eventually moved to Florida to help with the 1971 PGA Championship, where he went to work for Nicklaus.