Minister says he heard after action had been decided, and did not advise Cabinet.
Foreign Affairs Minister Murray McCully was briefed on the need to seize Kim Dotcom's assets at the time his officials were worried rejecting requests might upset the United States.
But Mr McCully said his role was confined to being briefed - and the discussions happened after the raid on Mr Dotcom's mansion.
Few details have emerged of how New Zealand's diplomats responded to the need to underwrite the US case with local taxpayer money.
The need to do so was driven by the Crown Law Office's failure to use the right restraining order to seize Mr Dotcom's property. They were meant to give notice of the seizure but deprived the internet tycoon of the ability to challenge the order.
It forced the Crown to go back to court and seek a fresh order.
Ministry of Justice staff handled the case and could have rejected it, meaning Mr Dotcom would have kept his New Zealand-based assets, which included his car collection, a $5 million property neighbouring his rented mansion and $10 million in government bonds.
Crown Law Office criminal leader Madeleine Laracy wrote on March 5: "Penny Ridings [international legal adviser from Mfat] will be there to enunciate the implications in terms of the diplomatic relationship with the US were NZ for this reason not able to pursue [the restraining order]."
Details released through the Official Information Act show Mr McCully was briefed on three occasions in relation to the undertaking between March and July.
In an emailed statement, Mr McCully said he learned about "the action against Kim Dotcom for the first time after the raid had commenced on his Coatesville property". He said he had offered no advice to the Cabinet on the Megaupload case and had not discussed it with US Ambassador David Huebner or officials from the State Department.
The underwriting of the US seizure with New Zealand taxpayer money involved consultation with at least three other Cabinet ministers. It had to be signed off by Finance Minister Bill English. Minister of Police Anne Tolley and Minister of Justice Judith Collins were also briefed, as was Attorney-General Chris Finlayson.