Businessman Sir Tom Farmer is to donate £100,000 to the Scottish National Party ahead of next year's Holyrood election.
Sir Tom said the SNP should have a "level playing field"
The multi-millionaire Kwik-Fit founder wants the nationalists to be able to compete with the resources of their better-funded political opponents.
The philanthropist said he had not made up his mind on who he would vote for.
Sir Tom said: "I consider it would be an unhealthy situation if the SNP were not able to actively campaign and participate in these debates."
The announcement came a day after party leader Alex Salmond revealed only a quarter of its targeted £1m fighting fund had been raised.
Sir Tom said: "I am not a member of the Scottish National Party, but I listened to the presentation made to me by Alex Salmond and his SNP team and concluded there should be a real open debate for the future of Scotland.
'Argument for independence'
"They should be on a level financial playing field with that of other major political parties."
Mr Salmond said he was "very grateful" for the donation.
"This is a tremendous boost for the party and not just in financial terms," he said.
"Sir Tom Farmer is one of the country's most respected and popular businessmen.
"The fact that he sees merit both in our policy ideas, and in the argument for independence, will be highly influential in the coming debate."
Mr Salmond, a well-known Hearts supporter, laughed off suggestions that he may be forced to switch allegiances after the donation from the Hibs owner.
Sir Tom founded Kwik-Fit in 1971 and its sale seven years ago to Ford made him one of Scotland's richest men.
He has also won the Carnegie medal for his philanthropic efforts through the Farmer Foundation to provide support to local communities, both at home and abroad.