SDLP leader Colum Eastwood has confirmed that he is standing down as party leader, saying that the "moment has come to step aside".
He told reporters in Co Derry that after nine years it was time to pass the baton on to someone else.
He said it had been his own decision and he now wanted to concentrate on representing the people of Derry in his Foyle constituency and working to deliver what he described as a "new Ireland".
He also endorsed fellow SDLP MP Claire Hanna as the next leader.
Mr Eastwood will remain in place as leader until the party conference on 5 October.
"The bottom line, though, was this last few years has been a period of immense change across these islands.
"What we have seen after Brexit has been really unstable in many ways, but [it has] also been a moment of opportunity.
"And now that we have the three strands, all the institutions of the Good Friday Agreement in a better place, in a more stable place, this is also now a big moment, I think, of change for this island, and I, for one, want to give my full commitment to leading in that space.
"The moment now has come for me to step aside, to allow other people to take on that mantle, to allow myself actually to focus on things that I need to focus on, primarily representing the people of this city, but also making the case for a new Ireland, making the case for change across this island.
"That's the work that I'm very passionate about. That's the work that I'm committed to do.
"So today, I have told the party chairman that I will be resigning as leader of the SDLP at the upcoming party conference on the 5th of October, and being there as a loyal servant of the party and to the next leader, I look forward to working with the new leader."
The 41-year-old took over the leadership of his party in 2015 and is an assured media performer. He has been the MP for Foyle since 2019.
On that occasion he won the seat back for his party from Sinn Féin with a whopping 17,000 majority amidst Brexit uncertainty.
He was re-elected in July's Westminster election but saw that majority reduced to 4,000 votes. Despite his relative youth he is a party veteran, having held elected office for almost two decades.
He said he had been attracted to the party by the work of former leader John Hume and his deputy Seamus Mallon.
Mr Eastwood joined in 1998 while just a young teenager to campaign in favour of the Good Friday Agreement.
The party has been under constant pressure since and has been overtaken by Sinn Féin as the dominant force in northern nationalism.
In recent years it has had to deal with some bruising electoral results.
The 2022 Stormont Assembly election saw it lose four seats to finish with eight, meaning that it had to go into opposition rather than form part of the mandatory governing coalition.
The following year, council elections saw another setback as Mr Eastwood's party lost 20 seats, dropping to 39 overall and leaving it in fifth place of the five main parties.
The recent Westminster election brought a reprieve as he held his MP's seat, despite a Sinn Féin push to win it back.
On taking up his seat last month he described the MP's oath of allegiance to the British king as "an empty formula" and said he was taking it under protest. He added his true allegiance was to the people of Derry and Ireland.
SDLP MLA for Newry and Armagh Justin McNulty said he was surprised by Mr Eastwood's decision.
He said Mr Eastwood had given a great deal to the party and that it was a "sad day".
He told RTÉ's Drivetime: "It is a bit of a shock to the system when your leader decides to step down."
Mr McNulty said Mr Eastwood was a standout leader who "hasn't put a foot wrong" while under intense scrutiny from the public and media.
He said Mr Eastwood had always spoken "truth to power".
Mr McNulty added that Ms Hanna would make a wonderful leader, but there were other potential candidates as well.
When asked if he would put his name forward for the position, Mr McNulty said he probably already had "enough balls in the air".
In a statement, Taoiseach Simon Harris said: "Colum has served with distinction and has been a progressive, responsible and pragmatic voice on all issues, but especially the challenging ones.
"During Brexit, Colum served the entire island of Ireland with distinction in Westminster with passionate, timely and informed interventions in debates that otherwise neglected the peace process. For that, we all owe Colum a debt of gratitude."
President Micheal D Higgins said Mr Eastwood made a "significant contribution to politics and to the development of peace and reconciliation".
In a statement, Mr Higgins said that Mr Eastwood's leadership over the past nine years alongside his service to his community at every level showed a "deep commitment".
"Colum Eastwood’s contribution to public service is extensive," he said.
"I wish Mr Eastwood good health and fulfilment in the next chapters in his life," he added.
Mr Eastwood's resignation means that both the SDLP and the Ulster Unionists are looking for new leaders at the moment.
Mr Nesbitt has already served as Ulster Unionist leader from 2012 to 2017.
The Ulster Unionists and the SDLP were the principal architects of the 1998 Good Friday Agreement which ended the Troubles but have found themselves supplanted by the DUP and Sinn Féin in the decades which followed.
