The First Minister told the Sunday Herald he was in favour of same-sex couples being allowed to wed in church, but opposed denominations being forced to allow such ceremonies.
He said he had not discussed the subject with Brian Souter, the millionaire boss of the Stagecoach group, who gave the SNP £625,000 during the 2007 election and is donating another £500,000 this year.
A member of the evangelical Church of the Nazarene, Souter bankrolled the controversial Keep the Clause movement in 2000. This tried to block the repeal of controversial legislation governing the discussion of homosexuality by local authorities and in schools.
Four of the five party manifestos contain proposals on gay marriage. Labour and the SNP say they will consult on the issue, while the LibDems and Greens say they would introduce gay marriage directly.
Only the Tory manifesto is silent on the issue.
As Salmond’s support goes beyond the manifesto, he stressed it was a personal point of view.
Nevertheless, it will be seen as a strong signal that the SNP is trying to shed its socially conservative image.
It was not until 2008 that the SNP had its first openly gay parliamentarian, when the MEP Alyn Smith came out. Surveys have found that Souter’s financial backing distances gay voters.
Asked if he was personally in favour of gay marriage, Salmond said: “I am.
“I’m very much against imposing it on any religion. But ... if a denomination is prepared to accept gay marriage then I’m in favour of it, yes.
“My personal feeling would be to tend towards it. But we’ll put it out to consultation.”
Marriage and civil partnership law is devolved to Holyrood, although some legal consequences of marriage -- such as tax, immigration and pensions -- remain reserved to Westminster.
Same-sex couples have been able to register civil partnerships since 2005.
However, the UK government is now consulting on allowing civil partnerships in church.
It also intends to consult on opening up civil partnerships to mixed-sex couples.
Earlier this year, the Equality and Human Rights Commission for Scotland recommended MSPs should legalise same-sex commitments in church, with a “conscience clause” letting reluctant churches, ministers and priests opt out.
Salmond added: “I was watching the debate south of the border [on the issue]. There is a canard running that denominations would be pushed into that position, but you just couldn’t do that.
“I would be extremely opposed to the idea of this being enforced on any unwilling denomination. That would be contrary to people’s ability to express their faith, which may not see the sacrament of marriage as being equivalent for a gay relationship, but ... if a religion or denomination has a different view, they should be able to express it.”
Asked if Souter would approve of his stance, Salmond replied: “I’ve never asked Brian.”
A 2009 poll found around two-thirds of Scots were in favour of gay marriage.
Tim Hopkins, director of the Equality Network, said: “We very much welcome Alex Salmond’s personal position on the issue. Whoever wins the election, we look forward to a consultation and then legislation.”
Labour leader Iain Gray said he “didn’t object” to gay marriage, but would not go beyond that.