Martin McGuinness, former IRA leader turned peacemaker, has confirmed he will not stand in the Northern Ireland Assembly election.
He quit as deputy first minister in a row over a botched green energy scheme, sparking an election on 2 March.
He had been in the post since entering NI’s power-sharing assembly in 2007 with ex-political enemy Ian Paisley.
Mr McGuinness, 66, has been ill for a number of weeks and said this was a factor in his decision.
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Mr McGuinness told the BBC that he had faced a “big decision” over his future and that he will never again be “an elected representative” in politics.
“The question I ask myself is: Are you capable, are you physically capable, of fighting this election with the intensity that elections need to be fought?
“And the honest answer is that I am not physically capable or able to fight this election, so I will not be a candidate.”
He added that his successor as Sinn Féin’s leader in Northern Ireland would be announced “next week”.
Democratic Unionist Party (DUP) leader Arlene Foster, who lost her position as first minister when Mr McGuinness resigned, said that he had been a “major figure” in Stormont.
‘Polar opposite backgrounds’
“While never forgetting the past, I believe the work at Stormont provided the foundations for our relative peace today.
“Despite all that has happened, I wish Martin McGuinness a speedy recovery and that he and his wife are able to enjoy time with their family away from the relentless focus of public life.”
Former first minister Peter Robinson, who worked with Mr McGuinness at the head of Northern Ireland’s government for seven years, said: “We came from polar opposite backgrounds but built up a relationship based on doing the best we could for all our people.”
Taoiseach (Irish prime minister) Enda Kenny said that while he and Mr McGuinness “may not always have seen eye-to-eye on every issue” he would “readily acknowledge the remarkable political jounrey that he has undertaken”.
Northern Ireland Secretary of State James Brokenshire said he was “sorry to hear” about Mr McGuinness’ decision.
Details of Mr McGuinness’ condition have not been disclosed officially by Sinn Féin but Irish national broadcaster RTÉ has reported that he has a rare heart condition.
Mr McGuinness said the illness had taken its toll but that he was “determined to defeat it”.
“I’m also very determined to continue to play a political role – it won’t be an electoral role although in the election I will be wholeheartedly behind the Sinn Féin candidates and the new leadership.”
Sinn Féin president Gerry Adams expressed his “heartfelt thanks” to Mr McGuinness and said he needs to take “time out to get better for himself, for his family and for our struggle”.
“On behalf of Sinn Féin and republicans everywhere I want to send him our best wishes.
“Give him the space to get better and (we’ll) increase our efforts so that when he returns the process of change has advanced.”
Mr McGuinness resigned in protest after former first minister Arlene Foster refused to step aside for an investigation into a Renewable Heat Incentive (RHI) scheme.
The row over the scheme surfaced a range of other issues, including the Irish language and gay rights, that divide Northern Ireland’s two power-sharing parties – ther DUP, led by Mrs Foster, and Sinn Féin.
Mr McGuinness’ resignation, and Sinn Féin’s refusal to nominate a replacement seven days later, has led to a snap Northern Ireland Assembly election on 2 March and the fall of the Northern Ireland government institutions.
The former deputy first minsiter said the institutions are “restorable” after March’s election but it will pose “particular challenges to everybody, but more so the DUP”.