"Our generation worked hard, we paid the taxes to build our existing assets. They are not for sale, they belong to all residents of New Zealand", he said to cheers and applause from the crowd.
He said the involvement of the New Zealand Students Association as well has his own organisation, showed that "we are united from the elderly to the younger generation" against the asset sales.
Labour Leader David Shearer thanked all the volunteers who gathered signatures over ten months and those who signed.
"This is about the transfer of an asset we all own into the hands of a very few. It's about fairness."
The referendum, "will make the Government listen to New Zealanders".
"The fight will go on - it's not finishing today. We in the Labour Party will continue to fight this until 2014."
Green Party Co-Leader Russel Norman said the massive piece work was done on behalf of the millions of New Zealanders opposed to asset sales and also for future generations.
"It is despicable that the Prime Minister then says that the people who signed this petition were tourists and children."
"Prime Minister you do not know New Zealanders. If the Prime Minister of New Zealand thinks that the 400,000 people who signed this petition are not real New Zealanders then he is in the wrong country."
The petition will be officially presented to Parliament's Clerk of the House this afternoon.
Finance Minister Bill English this morning told TV3's Firstline the petition would not sway his Government.
"We've already launched the Mighty River Power float and there will be others. This is an issue that was campaigned on right through election year.
"We laid out the policy in detail, the opposition parties had a year to debate it and they didn't win the election. So we're proceeding with the sakes on the basis of that mandate."
Mr English said the petition had gathered more than 300,000 signatures in a year, while more than 250,000 people had registered to buy Mighty River shares in 10 days.
But Peter Conway of the Combined Trade Unions told the crowd at Parliament this afternoon that the petition would have gathered signatures faster if it had a million dollar advertising budget and could gather signatures online as had been done for the Mighty River pre-registration.
It could take two months for the signatures to be officially counted.
Once a verified petition was reported back to Parliament, the Government would have one month to determine how and when a referendum would take place. The referendum must be held within a year.