"Losing the symbolic heartland of its so-called caliphate in Iraq will serve as a severe blow to Isis fighters and its supporters around the globe."
Brownlee said a further $1.4 million contribution would be made through NZ Aid to the United Nations Funding Facility For Immediate Stabilisation.
"New Zealand remains committed to coalition efforts. Now is the time to demonstrate to Isis, through our ongoing commitment, that Iraq and the global coalition are dedicated to defeating the terrorist threat."
The defeat of Isis in Mosul comes three years after the militants took the city. The United Nations predicts it will cost more than US$1 billion to repair basic infrastructure in Mosul.
New Zealand troops have been based in Iraq and Camp Taji, just outside of Baghdad, as part of a joint mission with Australia to train members of the Iraqi Security Force.
Last year the Government announced it was extending the deployment by 18 months, until November 2018.