Kate Forbes has admitted she would have voted against gay marriage if she had been an MSP at the time legislation was passed.
The finance secretary, who announced today her campaign to become the next SNP leader, said she would have voted against the landmark equalities bill "as a matter of conscience".
But she insisted she would have "respected the democratic choice made".
Forbes' social views have become a talking point among SNP members as a result of her membership of the Free Church of Scotland.
"I believe that it should be a conscience vote because of its profound significance in all mainstream faiths," she told The Scotsman.
"I think for me, Angela Merkel is the example I would follow, I would have voted, as a matter of conscience, along the lines of mainstream teaching in most major religions that marriage is between a man and a woman.
"But I would have respected and defended the democratic choice that was made."
Legislation to introduce same-sex marriage in Scotland was passed in February 2014, with 105 MSPs voting in favour and 18 against.
Forbes was first returned to Holyrood at the 2016 election and was promoted to the Scottish Government Cabinet in 2020.
Ruth Davidson, a former Scottish Conservative leader who campaigned for equal marriage, said: "I'm not an in-depth student of the SNP membership, but I'm pretty sure that, with this, Kate Forbes has just set fire to her leadership campaign on the very same day as she launched it."
Monica Lennon, a Scottish Labour MSP, said: "The hard-won rights of LGBTQ people can never be taken for granted.
"This is not a retrospective issue. We still have more to do to make Scotland fairer, safer and more equal, including ending conversion therapy. I hope all candidates are committed to robust legislation."
Hannah Bardell, an SNP MP, said: "I have listened carefully to Kate Forbes.
"I believe firmly in respectful discourse and debate and I have to say I have a level of respect for her being so open and direct about her views and why she holds them but I disagree with her.
"However, I would have hoped that given Kate has so many friends, including myself, who are LGBTQ and hold her and her talents in such high regard, she might have tempered them or at least considered her response a little more carefully."
Forbes had earlier told BBC Scotland she also would have voted against the gender recognition reform (GRR) bill that was backed by a majority MSPs last year.
The finance secretary was absent from Holyrood at the time of the vote as she was on maternity leave after giving birth to her first child.
Humza Yousaf, the health secretary, the frontrunner in the race to become the next SNP leader after securing endorsements from several senior Nationalists.
Speaking on LBC Radio, he said: "I'm a supporter of equal marriage. Let me get to the crux of the issue that you're asking me.
"I'm a Muslim. I'm somebody who's proud of my faith. I'll be fasting during Ramadan in a few weeks’ time.
"But what I don't do is, I don't use my faith as a basis of legislation. What I do as a representative, as a leader, as a Member of the Scottish Parliament is my job is to bring forward policy and pursue it in the best interest of the country."
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