The former leader of Scottish Labour said she voted for the SNP in a protest vote against Brexit.
Kezia Dugdale who led Scottish Labour between 2015 and 2017 backed the SNP at the European Parliament election in 2019.
The former MSP is now director of the John Smith Centre at the University of Glasgow. She is no longer a member of the Labour party and is married to SNP education secretary Jenny Gilruth.
Dugdale, 42, claims that she has voted for Labour at every election since that.
Speaking to BBC Radio 4 she said: "I voted SNP once in my life and that was in the European Union elections immediately after Brexit, where I was so mad about Brexit.
"I felt I could vote for the SNP in that European Union election, because that in no way could be construed as a vote for independence.
"I felt that that was a safe thing to do. I voted Labour in every election since then, from the council to the Scottish Parliament, to the general election, I have used a vote for Labour."
In August last year, she said her stance on independence had "moved" as she could no longer argue as strongly for the union as she did in 2014, but was not necessarily ready to vote Yes in a referendum.
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Pro-union Scottish politicians were quick to criticise her admission.
Scottish Conservative chairman Craig Hoy told Sky News: "Pro-union voters will be dismayed that a former Labour leader could vote SNP and betray the union so easily."
Meanwhile Scottish Labour has called on voters to stand by the party when they next go to the polls.
Current Scottish Labour leader Anas Sarwar said he believes 28 Scottish seats are "in play" at the general election.
Last year, Labour held off the SNP to win the Rutherglen and Hamilton West by-election by 17,845 votes to 8,399 - a 20.36 per cent swing from SNP to Labour.
SNP leader Humza Yousaf said: "I don't fear a general election at all. I see it's a huge opportunity.
"There's no getting away from the fact that 2023 was a difficult year. I'm not going to treat you or your listeners as fools."
