According to a statement, the terms of the agreement call for New York Life to increase its ownership over a period of seven years to a majority stake. The parties expect to close the transaction on or near January 13, 2013. 

“We are committed to making strategic acquisitions that enhance our investment boutiques with a focus on strategies sought by our clients,” said said Yie-Hsin Hung, senior managing director and head of institutional investments within MainStay. 

MainStay has also launched a sub-advisory partnership with Cornerstone, in which it proposes to adopt the $330 million Keystone Large Cap Growth fund. Pending shareholder approval, the fund will become the MainStay Cornerstone Growth fund, of which Cornerstone will maintain responsibility for the day-to-day portfolio management.

MainStay Investments, the mutual fund distribution arm of New York Life, has over $63.5 billion in AuM, as at July 31. 

Cornerstone is led by chief executive Andrew Wyatt and president and CIO, Thomas Kamp.