Mr Key pointed to the $40 billion Maori economy, such as Ngati Apa's farming interests, and said they would miss out if New Zealand was not in the agreement.
"You have huge interests now through the treaty settlements process and they're going to get bigger. But nobody owes this country a living. We have to make our way in the world. And Maori have been some of the most successful hungry traders this country has ever produced.
There is nothing to fear in that."
Tainui's Rahui Papa had raised the trade agreement in his speech from the marae, asking Key to delay the signing until all New Zealand had a proper chance to debate it. Mr Papa said Maori were not necessarily opposed to the agreement, given they themselves had traded through history. However, he said not enough was known to make a call on it.
Mr Key said Treaty rights were protected in the agreement.
"Not a single part of TPP cuts across the Treaty of Waitangi."
The trade ministers of the 12 countries involved in the controversial trade agreement will meet at the Sky City Convention Centre to sign the agreement on February 4 - just two days before Waitangi Day.
That prompted speculation of protests at Ratana and Te Tii Marae elder Kingi Taurua warned the Government would not be welcome at Te Tii for Waitangi Day if the signing went ahead. Labour leader Andrew Little also described the timing and location of the signing as "arrogant provocation" given Waitangi Day was a day when sovereignty was top of mind.
Mr Key said earlier that the timing was driven by the availability of ministers from other countries and the Sky City Convention Centre was chosen because it could hold a lot of people and because of security arrangements, given the expected protestors.
He told media he believed TPP was very good for Maori and it would not roll over Treaty rights. Every trade agreement since 2001 had protected the Treaty.
Mr Key will also have to again confront the issue of water rights when the Government holds its meetings with the Iwi Leaders Group over Waitangi weekend. At Ratana, Mr Key pledged to honour Maori rights and interests in water where they existed.
The Government has ruled out any national settlement on water and maintains nobody owns it.