Sinn Féin MP Francie Molloy has said he will not be standing for re-election to Westminster.
The veteran Irish republican is one of the party's longest-serving elected representatives and has been MP for the Mid Ulster constituency since 2013.
He was first elected as a councillor in the 1980s and has also previously served as a Stormont assembly member.
Mr Molloy, 73, said he would "pass on the baton to a new generation with confidence".
"I will not be seeking re-selection for the next election," he said in a post on X, formerly Twitter.
"Representing Sinn Féin and the people of Mid Ulster for the past 39 years has been the greatest honour of my life."
I will not be seeking re-selection for the next election.
Representing Sinn Féin and the people of Mid Ulster for the past 39 years has been the greatest honour of my life.
I pass on the baton to a new generation with confidence.
It’s been a long road, but we’re almost there. pic.twitter.com/gqNMnKDX4h
— Francie Molloy MP (@FrancieMolloy) February 13, 2024
Speaking at Stormont on Tuesday morning, he added: "I think it's time for new blood to come into it.
"I think it's very important that we're continually renewing.
"I have done the job in regards to local councillor in Dungannon, an MLA for Mid Ulster, the MP for Mid Ulster and the deputy speaker in here [Stormont], so it's been a fulfilment right through the whole issue.
"At 73 years of age it's probably now time just to relax and open up in a different line and actually now to be free to say whatever I want to say."
A general election is due to be held in the next 11 months.
Mr Molloy was first elected to Dungannon District Council in 1985 for the Torrent area.
In 1998, he became a Stormont assembly member for Mid Ulster and held positions including principal deputy speaker.
He was elected to Westminster in 2013 in a by-election to replace Sinn Féin's Martin McGuinness, former deputy first minister of Northern Ireland's power-sharing executive.
'Continue to make a contribution'
First Minister Michelle O'Neill, Sinn Féin's vice-president and an assembly member for Mid Ulster, paid tribute to her long-time friend and colleague.
"Francie Molloy has made a huge contribution to politics and the peace process here," she said in a statement.
"He was heavily involved in the early Civil Rights Movement, including the protest outside the Caledon Squat in 1968 which is often considered as the spark for people in their demand for better housing, better jobs and civil rights."
She added: "I have worked closely with Francie for many years and I'm confident that though he is retiring, he will continue to make a contribution in promoting equality for all in the time ahead."
Northern Ireland elects 18 MPs to the House of Commons.
The Democratic Unionist Party (DUP) currently has eight seats and Sinn Féin holds seven, while the Social Democratic and Labour Party (SDLP) has two and the Alliance Party holds one seat.
In January, Sinn Féin MP Michelle Gildernew announced she would be running for a seat in the European Parliament.
She will contest the Midlands-North West constituency, with elections scheduled for 7 June.