GIC has valued the whole group, a former unit of The Financial Times Group, at about 1 billion pounds, the sources said, adding the deal will probably be signed on Friday.

BC Partners bought the subscription-based news service from Pearson in a roughly 380 million pound deal in 2013. That was before the troubled education firm decided to part ways with the Financial Times in 2015 to focus solely on its core education business.

Selling a stake to GIC will help BC reduce its exposure to the group while raising cash to fund London-based Mergermarket's ongoing expansion.

Under BC Partners' ownership Mergermarket, known as an M&A news specialist, has embarked on a number of add-on acquisitions to expand its portfolio in adjacent areas, buying private equity-focused publications AVCJ and Unquote from Incisive Media among other deals.

BC Partners also held talks with Chinese media group Caixin about a possible sale of Mergermarket, another source said, but Caixin dropped out after a few weeks as it didn't believe it could secure enough financing for the deal.

BC Partners and GIC declined to comment while representatives at Caixin were not available outside regular business hours.

The deal with GIC, which was first reported by Sky News, follows the recent sale of oil price reporting agency Argus Media to U.S. investment firm General Atlantic for nearly 1 billion pounds in 2016.

(Additional reporting by Julie Zhu in Hong Kong and Anshuman Daga in Singapore; Editing by Susan Fenton)

By Pamela Barbaglia