Last night, Mallard used the legal immunity of parliamentary privilege to claim that a worker – who he apologised to for falsely accused of rape – committed sexual assault.
His rape claim previously led to a defamation payout of more than $300,000 to the worker.
The scenes in the House last night were rare, as Mallard was acting in his capacity as Minister of Parliamentary Services, and he was not chairing the session.
He had previously said the session would be "where the truth comes out" in regards to the issue.
PM's 'serious concerns'
In a statement before addressing media, Ardern said: "The serious issue of alleged sexual assault and harassment at Parliament was poorly managed and inappropriately politicised last night."
"Any investigation of claims of sexual assault should be in a manner that takes a victim-centric approach. It also needs to include principles of natural justice for the person allegations are made against."
She said she had spoken to Mallard about the matter and she, and by extension, the Government and the Labour Party, still had confidence in him as Speaker.
Now, she said, Parliament has an obligation to the public, to victims and to people who worked in the precinct was to "come together as a Parliament and sort it out".
"Resignations," she said, "will not resolve that".
Ardern also took aim at the Opposition.
Speaking to media this afternoon, Collins was highly critical of Mallard – her party has been trying to get rid of him as Speaker for months.
She said last night was a "disgraceful display from the Speaker," and added that Ardern had delivered Mallard a "slap on the wrist.
"She should have given him the sack … it should be a don't come in on Monday decision."
But she was full of praise for her own MPs, who participated in the debate last night, saying they conducted themselves strongly and "with courage".
"I was very proud of the work that our team did – particularly Chris Bishop and Michael Woodhouse in standing up for principles that we would expect in Parliament.
"What we need in Parliament is a speaker who can manage his, or her, emotions, to act in a professional manner and to bring back a degree of decorum in Parliament that has been sadly missing under his leadership.
Ardern said she had written to the Speaker and Deputy and Assistant Speakers asking them to reconvene the cross-party working group to consider how the Behavioural Standards can be given practical effect when Members of Parliament are dealing with sensitive staff conduct matters such as sexual assault.
