Police will not prosecute Meka Whaitiri after speaking to the press secretary she allegedly assaulted.
Private prosecutor Graham McCready made a formal complaint to police about the alleged incident on September 1.
On Tuesday they told him they would not take further action on his complaint.
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"The complaint was referred to the Investigations Group at Wellington Police District," police said in an email.
"The matter has been assessed and enquiries made with the alleged victim. Police will not be taking any further action."
Ms Whaitiri, a Labour Cabinet minister, was stood down by Prime Minister Jacinda Ardern last week over what was referred to as a "staffing matter".
There have been unconfirmed reports that Ms Whaitiri is accused of pushing a press secretary during an argument.
She was the second minister to lose her portfolio in a week after the demotion of Claire Curran.
In response to police's refusal to take the investigation further, Mr McCready has issued a caution and warning under Section 116 of the Crimes Act to those involved with the inquiry.
That includes the Prime Minister, Minister for Ministerial Services Chris Hipkins, the Department of Internal Affairs and Ms Whaitiri herself.
He has accused them of attempting to conspire or conspiring to defeat justice, saying Ms Ardern ignored his "respectful submission" about the alleged assault.