Doak, 59, was chairman of Khan Resources Inc, a uranium exploration and development company with operations in the country. He was found dead in his room on the 16th floor of the Blue Sky hotel in the capital of Ulan Bator on Thursday morning.
Local police say a preliminary autopsy found there was no foul play, but added that a final autopsy report would be available in four days.
"Jim's contribution to the success of the company has been enormous," Grant Edey, Khan's president and CEO, said in a statement Friday.
"He will be sorely missed, both by the company and by me personally as Jim and I had become very close friends over the years we worked together."
The company was involved in the development of the Dornod uranium property in Mongolia and became embroiled in a dispute with the Mongolian government over the rights to mine the property. In 2009, the Mongolia government canceled Khan's licences over the Dornod uranium project, handing the asset to Russia's ARMZ.
The company took issue with that and took the government to an international tribunal. Last month, the government was ordered to pay about $100 million to Khan as compensation.
Doak started out as an analyst and later made a name for himself as a critic of Canada's corporate elite who was unafraid to put chief executive officers on the spot.
In addition to his role with Khan, Doak was also president of L'Alliance Francaise de Toronto and was president and managing director of Megantic Asset Management Inc. from 2002 until last year.
Previously he founded Enterprise Capital Management Inc. where he served as the president and managing partner from 1997 to 2002 and had also served as a vice-president of ScotiaMcLeod Inc., and of First Marathon Securities Ltd. and had more than 25 years of experience as an economist and chartered financial analyst.