The news will come as a welcome morale boost to the Tories - still in shock from their defeat and from the subsequent resignation of William Hague.
But some Conservatives say the party should concentrate on grass roots fund-raising rather than relying on big donations.
In a statement released by the Conservatives, the philanthropist said: "Like many millions of people, I was bitterly disappointed that the Conservative election campaign was not more successful.
Way of life
"However, the Conservative Party, in my view, is the party best equipped to defend the British way of life.
"I hope that my donation will help to enable a new leader to deliver a Conservative victory at the next election."
The disclosure of the donation comes only hours before shadow chancellor Michael Portillo is expected to confirm that he will be standing for the party leadership.
If Mr Portillo does make his expected announcement, he will be the first Tory to throw his hat into the ring.
Other likely challengers could include shadow home secretary Ann Widdecombe and shadow defence secretary Iain Duncan Smith.
Deserving causes
Sir John Paul Getty, heir to an oil fortune, received an honorary knighthood in 1986 and became a British citizen in 1997.
He is reported to have given away more than £120m to deserving causes in Britain.
He gave £50m to the National Gallery, £20m to the British Film Institute, and millions in smaller donations, often anonymous, to other charities and causes.
Criticism
John Strafford, chairman of the Campaign for Conservative Democracy, argued both the Tories and Labour should not accept big donations.
"Big donations buy success, buy influence and sometimes they buy power," he told BBC Radio 4's Today programme.
Mr Strafford, who did not doubt Sir John Paul Getty was a "decent man", said he would be quite happy for the Conservatives to return the money.
"It demotivates ordinary members of the party going out and raising funds themselves," he continued.
He said the Tories should follow the example of Lord Woolton, who by organising a grassroots fund-raising drive after the Tories' 1945 landslide defeat vastly increased the party membership.