A US investment firm has also agreed to snap up a 1.2 billion dollar stake in Merrill while Temasek may increase its shareholding by a further 600 million dollars.
Merrill executives said the cash injections would help it shore up its stressed balance sheet.
The Dow Jones Industrial Average was up a strong 82.83 points (0.62 percent) at 13,533.48 at 1616 GMT.
The tech-rich Nasdaq composite had gained 15.30 points (0.57 percent) to 2,707.29 while the Standard & Poor's 500 index spiked 8.89 points (0.60 percent) to 1,493.35.
Investors focused on Merrill's announcement as trading wound down for the Christmas Day holiday.
"John Thain, the former CEO of NYSE Euronext, stepped in to right the ship and he has wasted little time in str