Sinn Féin MP for Mid Ulster Martin McGuinness is to resign his seat, forcing a byelection, as part of a shake-up to end Sinn Féin dual mandates at Westminster.
Party president Gerry Adams said Sinn Féin's four other MPs will stand down from the Northern Ireland Assembly where new representatives can be put in their place without further elections.
Mr Adams said his party would continue to refuse to sit in Westminster, but wanted to avoid creating a string of electoral contests by resigning all five of its parliamentary seats.
Stormont politicians have been heavily criticised in the past for holding posts in local councils, the devolved Stormont Assembly and at Westminster.
Mr Adams said: "The key thing to be said about this issue is that other parties are talking about ending dual mandate, Sinn Féin has ended dual mandate."
The Sinn Féin MPs set to leave the Assembly are West Belfast representative Paul Maskey and West Tyrone representative Pat Doherty, plus former Stormont ministers Fermanagh-South-Tyrone MP Michelle Gildernew and Newry-Armagh MP Conor Murphy.
Mr Adams said his party had resolved the issue of Assembly members holding council seats, and was now dealing with MPs who sit at Stormont.
"We are today announcing that that is going to be phased out," he said.
He said Mr McGuinness had to remain in the Assembly because of his role as Deputy First Minister, while new Sinn Féin politicians would be co-opted on to the Stormont benches to fill the four vacant places.
Mr Adams said it was possible that at the next Assembly elections the MPs may choose to seek to return to Stormont.
But he said they would in the meantime continue to play leading roles in the party.
Mr Adams is a former MP and Assembly member for West Belfast and resigned the seats to successfully contest a parliamentary seat in Louth in the Irish Republic where his party has enjoyed increased support.
"Our party is developing across the island. We have a lot of work to do to meet our potential," he said.
He said of his MPs' future roles: "There will be lots of work to do in terms of both lobbying and policy.
"We will not be taking up seats at Westminster, just to make that clear. We also will be putting in place a programme of work across Britain strictly in relation to promoting the merits of Irish unity."
Mr McGuinness thanked all those who had voted for him since he took the Mid Ulster Westminster seat in 1997.
"I am in a different position from my colleagues, in that I will be continuing on as an MLA," he said.
"I want to take this opportunity to thank all of those people who supported me for the last 15 years in election after election.
"But my work on their behalf will continue in this Assembly."
PA