A formal complaint was laid with the general manager of Parliamentary Service about the person after Mallard's radio interview this morning.
"I am satisfied that the Parliamentary Service has removed a threat to the safety of women working the parliamentary complex.
"I want to thank the staff member [who laid the complaint] who has come forward .... This is obviously a very traumatic time for that individual, and will also be the case for other individuals, other women, who are involved."
He encouraged anyone who had been assaulted to ring the Safe to Talk line - 0800 044 334 - or contact police or the Parliamentary Service general manager.
"My appeal to the media is to let the process run and take care not to further traumatise either this woman or other women."
He said the person has been "stood down" while the employment investigation was underway.
He said it was up to the woman involved, not himself, to refer the matter to police.
He was not aware of the allegation, which was an assault of a sexual nature, before the Francis review.
He stood by his comments this morning that the incidents of sexual assault were tantamount to rape.
Asked if parliament was safe, Mallard said: "One can never make an absolute guarantee of that type, and clearly we have a lot of work to do out of the review around attitude."
But he said one of the dangers had now been removed from the premises.
Mallard said he understood that one person was responsible for the three serious incidents raised in the Francis review.
He said his comments this morning, as well as media coverage, had contributed to re-traumatising victims. "It would have been better if it had not played out that way."
He said a formal complaint was laid with the general manager of Parliamentary Service about the person after his radio interview this morning.
