The online business which sells discounted brands including Adidas, Nike, Ben Sherman and Quiksilver, is understood to have fetched a price tag of nearly £90 million.
Former Tesco Direct chief executive Steve Robinson has been drafted in as chief executive. The current chief executive Mike Tomkins will step down from the role to become a non-executive director. He has also reinvested in the business.
Tomkins led a management buyout of the business by ECI Partners in 2004, in a deal understood to be worth £35m.
TA Associates beat several other private equity and trade bidders, including Sports Direct owner Mike Ashley, to snap up M and M Direct.