New York-based Blackstone, which is about to go public, said Mulroney, prime minister from 1984 to 1993, will earn $100,000 a year as a Blackstone director.
Mulroney will also receive equity of 10,000 "deferred restricted common units" that vest over three years, The Globe and Mail in Toronto reported citing Blackstone documents.
Blackstone common shares are expected to be sold to the public at between $29 and $31 each.
Mulroney, a partner in Montreal law firm Ogilvy Renault, is also on the boards of gold-mining giant Barrick Gold Corp., communications company Quebecor Inc. and food processor Archer Daniels Midland Co.
He recently retired as senior adviser to Dallas-based private-equity fund HM Capital, earlier known as Hicks, Muse, Tate & Furst.
Two other Blackstone outside director appointees are retired Deloitte & Touche Chief Executive Officer William Parrett and British investment banker Nathaniel Charles Jacob Rothschild of the prominent Rothschild family of bankers, Blackstone said.