Peter Robinson is to step down as Northern Ireland's First Minister and leader of his Democratic Unionist Party.
In a widely expected announcement, Mr Robinson, 66, said he will not contest next May's Assembly election and is likely to leave office in the coming weeks.
The move comes days after he signed a political deal with Sinn Fein and the UK and Irish governments.
Mr Robinson said he had wanted to stabilise the powersharing administration in Belfast before stepping aside.
The veteran politician suffered a heart attack earlier this year but has insisted he had made his mind up to leave before the health scare.
There had been growing speculation Mr Robinson would outline his departure plans at the DUP's annual conference this weekend.
In the event, he confirmed his exit in a pre-conference interview with the Belfast Telegraph.
"I think it would be disrespectful to the party membership if I was to go through a conference with the pretence that I would be leading the party into the next election," he said.
"I think they have a right to know what the circumstances are."
North Belfast MP Nigel Dodds will be among the favourites to take over as DUP leader.
However, with Mr Dodds based in Westminster, another senior party figure could take on the role of Stormont First Minister.
Finance Minister Arlene Foster has been touted as a potential leader of the powersharing coalition.
Mr Robinson said he would remain in the post until Tuesday's Fresh Start agreement is "bedded in" - a period he indicated could last into the early new year.
"There are a number of fairly immediate decisions that have to be taken and they (party officers) will then organise a transition," he said.
"In the meantime, I don't want people to be focusing on issues of succession yet. When the party officers declare the process - which I guess would be at the beginning of next year - then people can start looking at who the successors should be for leader and first minister. Let's focus on the agreement and getting it bedded in."
Mr Robinson, who replaced Ian Paisley as first minister and DUP leader in 2008, said he had wanted to secure a number of specific objectives before leaving - namely stabilising the powersharing government, the DUP retaking the East Belfast Westminster seat he lost in 2010 and setting a date for Northern Ireland to determine its own corporation tax rate.
With all those accomplished, he said the time was right to step aside.
"For anyone who is not very young to go beyond two terms is stretching it," he said.
"There are massive pressures on anybody in this job. You do need to renew political leadership, bringing in people with perhaps more energy and people with new ideas."
During a heated Stormont debate on Wednesday, on a motion to allow Westminster to legislate to introduce stalled welfare reforms in Northern Ireland, a number of political opponents suggested the Assembly vote was being rushed through to leave the stage clear for Mr Robinson to make his statement at his party conference on Saturday.
Tuesday's Fresh Start agreement resolved the wrangle over the non-implementation of the UK Government's welfare reforms, and a number of other disputes which had pushed the coalition Executive to the verge of collapse, including the fall-out from a murder linked to the Provisional IRA and an acute budgetary crisis.
However, the accord has been fiercely criticised by victims' campaigners for failing to secure consensus on new mechanisms to address the legacy of the Troubles.