Thousands armed with banners and umbrellas braved the rain, urging the Government to hang the proposed Trans-Pacific Partnership free trade deal out to dry.
Protesters have turned out in their thousands at rallies around the country today, ending an action week by those opposed to the proposed deal.
Organisers estimated that 10,000 people packed into Auckland's Aotea Square before marching down Queen St to Customs St, where they chanted outside the United States Consulate General.
"John Key don't be a Don Key", "TPPA = Death to Democracy" and "TPPA Walk Away" were among the slogans on display.
There were no incidents at the Auckland protest, and police said they were pleased by the peaceful demonstration.
Meanwhile an estimated 3000 protesters marched from Wellington's Midland Park, including some wearing giant masks of Prime Minister John Key and Finance Minister Bill English - and gathered outside Parliament.
About a dozen police officers - some in helmets - stood guard along the parliamentary steps, although one woman managed to give them the slip and made it to the top of the steps.
Inspector Chris Bensemann said police were called to assist security after she pushed through the barriers, but the protester was ultimately moved on and no arrests were made.
It's Our Future spokesman Edward Miller, who helped organise the protest, said he was "absolutely thrilled" with how it went.
The US Consulate General in Auckland had warned US citizens to stay away from the Auckland march, telling them "even demonstrations intended to be peaceful can turn confrontational".
But Mr Miller said he was thankful to the Consulate for raising the profile of the protests, which he said had mobilised a huge number of people behind one cause.
About 2000 people turned out in Christchurch, 800 in Nelson and others turned out at rallies in Dunedin, Kataia, Hokianga, Whangarei, Hamilton, Colville, Tauranga, Whakatane, Napier, New Plymouth, Featherston, Timaru, Little River and Invercargill.
The most recent round of TPP talks in Hawaii failed to net a final agreement but trade ministers from the 12 countries have said they are still highly confident a deal can be reached.
The TPP would cover the United States, Australia, New Zealand, Japan, Canada, Brunei, Chile, Malaysia, Mexico, Peru, Singapore and Vietnam.
The protesters say the TPP isn't in New Zealand's best interests and they want the Government to back out of it.