Lord Ashcroft is donating £2m to create a "fighting fund" to help local Tories fight Labour in marginal seats.
Lord Ashcroft was Tory Party treasurer
The ex-party treasurer said Tory associations in the key battlegrounds will have to apply direct to him for a share of the money.
His decision to bypass Conservative Central Office was because the Tory target constituencies needed the cash.
He said 85% of Tory constituency agents were based in safe seats with only 19 full-time agents in marginal seats.
He told the BBC Radio 4 Today programme: "What I have done following Michael Howard's election is to pledge a £2m fighting fund to go directly into
the marginals, into the constituencies that we have to win in order to significantly reduce [Labour's] majority at the next election or even go for
He added: "The constituencies in the marginals may
approach myself in order to give to me their business plan... in order to make a mark in those constituencies."
Lord Ashcroft said the Tories had to win more than 150 marginal seats - in what he dubbed an electoral "war zone".
The multi-millionaire businessman indicated his support for Michael Howard, who announced his shadow cabinet on Monday.
Howard's shadow cabinet is being announced on Monday
"Michael is a genuine heavyweight, substantial political experience," he said.
"I think from the speeches that he has made recently he has been admitting some mistakes, he has mellowed, and I think he has all the attributes to take the fight to Labour.
"And so long as the Conservative Party unites behind him, I think that will be an additional strength."
Another big Tory donor, Stuart Wheeler, said he backed Mr Howard.
Mr Wheeler, who gave £5m to Conservatives ahead of the 2001 general election, also said he would now be prepared to donate more cash.
The betting tycoon had previously said that he would not give his money to the Tories while Iain Duncan Smith remained leader.
That announcement contributed to the momentum that eventually saw Mr Duncan Smith ousted in a confidence vote.
On Monday, Mr Wheeler said: "I am certainly not going to write as big a cheque as I did 2-5 years ago because I am nothing like as rich as I was then.
"But I would expect to make let's say a significant donation."
John Madejski, chairman of Reading Football Club and a former big donor, said he would wait and see before promising more funds.
He told BBC Two's Newsnight: "As I understand it, people have already been pledging a lot of donations to the Tory party since the change and that bodes well.
"But I shall see how things turn out in the future and act accordingly."