Aon Corp , the world's largest insurance brokerage, said it will acquire human-resource service company Hewitt Associates Inc for about $4.9 billion in cash and stock to beef up its consulting business.

Aon's offer of $50 a share is 41 percent more than Hewitt's closing stock price on Friday.

The deal will help Aon get a firm foothold in human resource and benefits outsourcing and take on rival insurance broker Marsh and McLennan's Mercer unit.

Aon plans to integrate Hewitt with its existing consulting and outsourcing operations and sees annual revenue of $4.3 billion for the combined entity, which will be named Aon Hewitt.

Russ Fradin, chairman and chief executive officer of Hewitt, will head Aon Hewitt.

Aon expects the deal to add to 2011 and 2012 earnings and generate about $355 million in annual cost savings in 2013, primarily from reduction in back-office areas.

The Aon-Hewitt deal is the second major deal in the consultancy space in a year after Towers Perrin and Watson Wyatt agreed to a $3.5 billion merger to create the world's largest HR consultants.

The insurance brokerage expects to finance the deal through a $1.5 billion bridge facility and $1 billion bank term loan.

Shares of Hewitt rose more than 30 percent in trading before the bell after closing at $35.40 Friday on the New York Stock Exchange. Aon shares closed at $38.34 Friday.

(Reporting by Amulya Nagaraj and Abhinav Sharma in Bangalore; Editing by Saumyadeb Chakrabarty)