Labour President Nigel Haworth has resigned over his handling of sexual assault allegations.
Haworth offered his resignation to Ardern after she read correspondence to the party confirming that the complaints were very serious.
Nigel Haworth has been Labour Party president since 2015.
Ardern made her displeasure with Haworth clear, saying "mistakes were made".
It follows reports by Stuff that a former Labour party volunteer says he raised these allegations with Haworth.
Haworth issued a statement on Tuesday claiming a 19-year-old woman did not tell him she was sexually assaulted by a Labour staffer, when they met in August 2018. He also said the accusation was also not provided to a panel established to investigate the man's conduct.
Prime Minister Jacinda Ardern has repeatedly said she was not told the allegations were of a sexual nature.
Stuff's story appeared to contradict that.
- 'Total disbelief': Labour Party volunteer alleges sexual assault
- Emails show Labour was sent details of sexual assault allegations against party staffer
- Former Labour party volunteer says he raised allegations with party president Nigel Haworth
- Jacinda Ardern: 'I never knew the complaints were of a sexual nature'
Haworth has held firm and maintained he acted professionally throughout the saga, disputing claims that he was told about sexual assault allegations.
Ardern said on Wednesday harm had been done and she was taking a victim-centred approach.
When asked if Haworth knew about the sexual assault allegations and had misled her, she said he maintained his position throughout and continued to do so.
The Party and Haworth maintained none of the complainants went directly to them claiming they had been sexually assaulted, she said.