Maori MP Hone Harawira will kickstart his new party by forcing a byelection in his Te Tai Tokerau electorate.
Mr Harawira launched his new Mana Party in Auckland this afternoon.
He told a gathering of about 300 people that he had always believed he was accountable to the people of his electorate. He believed they should be able to have their say on his new party.
He will officially resign from Parliament by writing to the Speaker on Monday, setting in train the process for a byelection.
Mr Harawira also said the Maori Party president told him last night that it would not stand a candidate against him this year.
When Mr Harawira left the party in February, they had agreed not to stand against each other in the Maori electorates.
However there had been uncertainty about whether the agreement would hold.
Mr Harawira's decision to force a byelection just seven months before a general election is likely to be criticised. Labour leader Phil Goff has already said he would view it as a "publicity stunt" and said it would be irresponsible and costly.
In his speech, Mr Harawira said his party would be more accountable to those who elected it.
"Let today be the day that we reject the politics of fear... Let today be the day we reject the politics of compromise because we deserve better than the weak accommodations we have now."
He also set out some policies, including nationalising assets such as power, water and housing and ending state asset sales. He said it would campaign on the so-called 'Hone Heke' tax - a financial transaction tax of one cent in the dollar.
He criticised spending such as "$36 million being wasted on this bloody yacht race in San Francisco."
Others speaking at Harawira's launch included potential candidates Annette Sykes and Mereana Pitman. Former Green MPs Sue Bradford and Nandor Tanczos also spoke, saying it was time there was a new force for workers on the left.