Jeremy Corbyn, a long-standing supporter of a united Ireland, has met with Sinn Fein leaders Gerry Adams and Martin McGuinness this week in Parliament.
The left-winger is now the frontrunner to become the next Labour Party leader.
A YouGov poll for The Times saw him top the ballot with the support of 43% of party supporters - way ahead of bookies' favourite Andy Burnham on 26%.
Mr Corbyn first met Gerry Adams in London in 1984, well before the IRA campaign ended in 1994.
And he was later accused of "traitorous" behaviour for helping Mr Adams plug his autobiography inside the Houses of Parliament in 1996.
Yesterday he demonstrated his continued support of the Irish nationalist cause.
Gerry Adams shared a picture of Mr Corbyn sitting around a table in Portcullis House enjoying coffee with the Sinn Fein president, vice-president Mary Lou McDonald, Martin McGuinness and Michelle Gildernew.
"With Jeremy Corbyn & the comrades @ Portcullis House, Westminster," he said.
The party were due to meet David Cameron last night to discuss welfare cuts.
Mr Corbyn was a supporter of the republican Troops Out movement during the Troubles, which campaigned for the Army to be withdrawn from Northern Ireland.
He reiterated his support for a reunified Ireland in a leadership hustings on Sunday.
Andrew Neil challenged Mr Corbyn during a Sunday Politics hustings debate, saying: "You didn't just deal with Sinn Fein, you dealt with the IRA. Three weeks after the Brighton bomb, in which the IRA had tried to destroy the democratically elected government of this country, you invited two convicted IRA terrorists to the House of Commons."
Mr Corbyn replied: "They were former prisoners who had come out of prison, women who had came out of prison to Parliament, actually to a meeting that had been arranged long before, to talk about prison conditions and rehabilitation of prisoners. Is there anything wrong with that since they had a spent conviction?"
Neill: "Their organisation had just tried to blow up the British Government, did you not think about that?"
Corbyn: "Of course I thought about it and I wanted a peace process. That's why I maintained a level of contact with Sinn Fein throughout that period, as indeed secretly the British Government did..."
Neill: "You didn't want a peace process, you wanted a united Ireland. You saw Northern Ireland as an imperialist, colonial situation."
Corbyn: "I do believe ultimately that Ireland should be reunited, but I also never believed there was going to be a military victory for either side in Northern Ireland.
"There had to be a peace process and there was a peace process and I am not ashamed of those of us that had the courage to step outside and say there has to be discussions with people... in order to being about a ceasefire which did indeed happen and the second ceasefire finally brought about the Belfast Agreement. Surely that is a good thing and actually a great achievement for Mo Mowlam and that Labour government."