Media reports on Tuesday revealed the state's Labor Party was investigating allegations of inappropriate behaviour by Mr O'Byrne when he was head of the Liquor, Hospitality and Miscellaneous Union.

It was understood he sent sexual text messages, and kissed a woman without her consent.

Responding to the accusations on Tuesday afternoon, the newly-elected leader said he initially believed the exchanges between himself and the employee were consensual.

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"While I have not yet received a copy of the complaint I believe it necessary to publicly respond to some of the matters reported today," Mr O'Byrne said.

"I acknowledge my behaviour did not meet the standards I would expect of myself. I also acknowledge I have let down my wife and my family.

"At the time of the reported events I genuinely believed the kiss and text exchanges to be consensual. However, I now understand that this was no the case.

"I have written to her to offer my unreserved apology for the unwanted contact and texts. I genuinely thank her for having the strength to bring this issue to light and I also thank other women who have advocated and spoken about their personal experiences to inform the current national conversation about consent."

Mr O'Byrne will stand down until the investigation is complete.