The Lib Dem Scottish spring conference passed a motion yesterday calling on the Scottish government to legalise gay marriage.
Party activists said the current system was “discrimination that needs to end”, Press Association reports.
The motion also called for straight couples to be given the option of civil partnership ceremonies.
Edinburgh West MSP Margaret Smith told the debate she was in a civil partnership but had been “denied the right to be married in church”.
Ms Smith, who is religious, told the conference in Perth that there was “no true equality” while gay couples were barred from marriage.
Last month, federal Lib Dem leader Nick Clegg told PinkNews.co.uk readers that he supported gay marriage.
He said: “Love is the same, straight or gay, so the civil institution should be the same, too. All couples should be able to make that commitment to one another.”