TNS Inc TNS.N, which provides data transmission services to banks and retailers, agreed to be taken private by an investor group led by Siris Capital Group for about $518 million.
The cash offer of $21 per share represents a premium of about 44 percent to TNS's closing price on Monday.
Including debt and cash, the deal is valued at about $862 million, TNS said.
The company, founded in 1990, provides secure data networks to credit card companies, payment processors, retailers and telecom companies.
Greenhill & Co LLC advised TNS on the deal, which is expected to close in the first quarter of 2013. UBS Securities LLC and Macquarie Capital were the financial advisers for Siris.
Shares of TNS, which last month reported third-quarter revenue of $137.2 million, were up about 45 percent at $21.07 in premarket trading on Tuesday.
(Reporting by Chandni Doulatramani in Bangalore; Editing by Saumyadeb Chakrabarty)