NEW YORK — Merrill Lynch & Co. said Wednesday it has tapped New York Stock Exchange head John Thain to lead the world's largest brokerage through the unfolding credit market turmoil that threatens Wall Street's biggest investment houses.

Thain, 52, has been selected to become Merrill's next chairman and chief executive officer. His appointment comes just two weeks after the ouster of Stan O'Neal as Merrill reported steep losses during the third quarter.

"I am excited and honored to have the opportunity to lead such an outstanding organization," Thain said in a statement. "I am certain that together we can continue to grow Merrill's global business and add value to our customers and our shareholders."

Thain, who is credited with remaking the NYSE into the world's first truly global exchange, is no stranger to the investment world. He started out on the bond desk at Goldman Sachs Group Inc. and left the firm as its chief operating officer.

"John Thain is the right person to become the new Chairman and CEO of Merrill Lynch. He brings unparalleled leadership experience and knowledge of the complexities of global capital markets as well as the skills required to operate a large financial services company," said Alberto Cribiore, Merrill Lynch's interim non-executive chairman and head of Merrill's search committee.