Alex Salmond has said he personally supports homosexual marriage, in comments which mean he has gone further than his party’s manifesto pledge.
The Scottish National Party (SNP) say they want to “begin a process of consultation and discussion” on the issue.
Asked whether he was personally in favour of same-sex marriage, Mr Salmond said: “I am”.
The SNP leader added: “My personal feeling would be to tend towards it. But we’ll put it out to consultation.”
Criticising the stance, a spokesman for the Roman Catholic Church in Scotland said: “These remarks are extremely unhelpful. A lot of Catholics will be dismayed by them.”
Tim Hopkins, Director of campaign group 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.”
Scottish Labour leader Iain Gray said he “didn’t object” to gay marriage, but would not go beyond that.
Scottish Labour’s manifesto says they want to consult on “options” regarding the controversial move.
The Scottish Liberal Democrats and the Scottish Greens have given their full support to same-sex marriage while the Scottish Conservatives’ manifesto is silent on the issue.
Scottish Parliamentary elections take place on 5 May. If marriage is redefined in Scotland, there will be pressure to enforce the redefinition throughout the UK.
The Christian Institute has produced a briefing on the issue, arguing for retaining the definition of marriage as the lifelong union of one man to one woman.
The taxpayer-funded Equality and Human Rights Commission in Scotland last month called on the next Scottish Government to alter the law on marriage. Its call was criticised as “partisan” and “ill-judged”.