Former Prime Minister Julia Gillard has angered some supporters of same-sex marriage after declaring she now supports it.

Ms Gillard announced her changed position delivering the Michael Kirby Lecture on Wednesday, while warning the idea of a plebiscite or referendum on gay marriage was illogical and dangerous.

The former Labor leader, who previously voted against gay marriage in parliament, said given the chance again she would vote yes.

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She admitted her previous position was considered odd and idiosyncratic given her broader values.

But Ms Gillard also defended her legacy, saying she assumed the Liberal party would permit its MPs a conscience vote and parliament would eventually allow for same-sex marriages.

“My position would have been overtaken by history, something which would have caused me no heartburn,” she said.

Australian Marriage Equality said Ms Gillard’s announcement was proof even high-profile opponents could open their hearts to change.

“But we urge other political leaders not to wait until it is too late for them to show leadership in parliament, as Ms Gillard has done,” director Rodney Croome said in a statement.

Others took to Twitter to denounce Ms Gillard’s changed position as belated.

“Gillard had her chance when PM and did nothing for SSM,” one wrote.

Ms Gillard also said a plebiscite or referendum on gay marriage were ideas of “superficial appeal and long-lived dangers”, warning such votes could undermine confidence in the parliamentary process.

She wants the matter to be resolved through a conscience vote by the parliament after the next election.

Ms Gillard recently sought legal advice over a quote used in an advertisement critical of same-sex marriage, which she considered was taken out of context and misused.