The decision comes a fortnight after the company's founder-chairman V.S. Siddhartha was found dead on July 31 in a river near Mangaluru on the state's west coast.
"Parleys with Blackstone were underway by Siddharth since January when he was looking at selling his or the holding company's equity stake to raise funds for pairing high-cost debts," a source told IANS.
The New York headquartered Blackstone specialises in private equity, credit and hedge fund investment strategies.
"The transaction is subject to completion of Blackstone's due diligence, documentation and receipt of regulatory approvals in the next 30-45 days," added the filing.
The board also approved disinvesting in its step-down arm AlphaGrep Securities Ltd to Illuminati Software Ltd for Rs 28 crore.
The 9-year-old Delhi-based IT firm is involved in data processing.
"The twin transactions will help in deleveraging the Coffee Day Group, and ensure smooth operations while safeguarding the interests of stakeholders, including investors, lenders, employees and customers," added the filing.