Government backing was proof to other funders they were "backing a winner", with Foundation North and Lotteries named by Mr Trass as other potential funders.
Mr Trass said the Hundertwasser funding and other projects announced as part of the overall Tai Tokerau plan marked a "new era" for Northland, although Whangarei District Councillor Stu Bell said the money would be better spent elsewhere.
"As an economic development project I think it's just crazy, when you think about what else we've got on in Northland that needs addressing."
While the centre's running costs would be underwritten by the trusts involved by up to $500,000 each year if it could not turn a profit, Cr Bell said this might not be enough.
"Media reports say the [Hundertwasser Museum] in Vienna cost the council €400,000 a year to keep it going," he said.
"Admittedly, visitor numbers were less than what was predicted here so our 'experts' may have it right. But I do worry about who is going to pick up the tab."
Whangarei's National MP Dr Shane Reti was among the centre's major backers and had lobbied Government to give it a cash injection, while Mayor Sheryl Mai was a long-term advocate.
While only $532,667 of the $10.2 million is "in hand", pledges include $2.97 million set aside in Whangarei District Council's Long Term Plan, $4 million from Government, and $1 million from a trust.
The $16.25 million also covers $1.1 million which has already been spent by WDC on consent for the project, prior to it being taken over by trusts.
Project director Andrew Garratt said whether the money was pledged or "in the bank" had no bearing, as all pledges were recorded through legally binding documents.
It was usual for projects of this type to take pledges, rather than donations, until it was 100 per cent certain they would proceed.
Online reader comments following the Thursday announcement ranged from congratulatory to "it's all right for the Government to give it money, it's in Wellington and doesn't have to look at the stupid [thing] every day".
A June 2015 referendum of Whangarei residents brought a final decision on whether or not the centre should go ahead - a debate which had plagued the town for more than 22 years.