Mirror Group already owns The Sporting Life, which covers horse racing, greyhound racing and sports betting, and the two papers will retain separate editorial teams and identities, Mirror Group said.
The Post will focus on horse racing. The title was launched in April 1986 and is owned by the Maktoum family of the Arab Emirates, who run a global racehorse empire.
A spokesman for the Mirror Group, which owns 46 per cent of Newspaper Publishing, publisher of The Independent, said yesterday: "The Racing Post will continue to be a pre-eminent newspaper for the racing fraternity and The Sporting Life will broaden its content and appeal with wider coverage of sporting activities."
The spokesman said that the deal is subject to formal approval by the President of the Board of Trade. He added that it was not possible to give any further details, including the price of the deal.
There will be a short period during which the Racing Post will continue to be published from its present offices in South-west London, after which staff will be transferred to Mirror Group's headquarters at Canary Wharf, in London's Docklands.