Betfair, the biggest online betting company, will hand over a £6m lump sum to the Horserace Betting Levy Board this month.
The donation makes Betfair the first major operator not under a UK licence to commit a sum equal to the levy requirements. Betfair moved off shore to Gibraltar this year and therefore was not required by law to pay the levy.
Martin Cruddace, the company's chief legal and regulatory officer, said: "Betfair has a strong track record in supporting British racing and this substantial figure is testament to the commitment we have in seeing the sport thrive.
"I would now encourage those other operators not licensed in the UK but who are taking bets on British racing to follow suit. Racing in this country is facing a challenging time but this donation will help to further support prize money and investment in the sport."
The figure is equal to the money that the company would have been required to pay in the terms set out for the 50th Levy Scheme for 2011-12. It is also paying the full amount in one lump sum rather than in the usual instalments.
The £6m is the largest single amount the Horserace Betting Levy Board has ever received.