Sinn Fein's Martin McGuinness will meet the Queen next week and shake hands in an historic first for the Northern Ireland peace process, the party has confirmed.
The Deputy First Minister at the Stormont executive will attend a cross-border event in Belfast on Wednesday, which the President of Ireland, Michael D Higgins, will also attend.
Sinn Fein president Gerry Adams said the decision had been taken after consulting with grass roots support and allowing the party's ruling council, the ard comhairle, to decide at a four-hour meeting in Dublin.
Mr Adams said: "This will understandably cause difficulties for some republicans and nationalists, especially for those folks who suffered at the hands of British forces."
He said Sinn Fein wanted to see a new republic in which the traditions of orange and green could be brought together in a cordial union. The ard comhairle decision was not unanimous but was a clear majority, the party confirmed.
Leading cross-border charity Co-operation Ireland is to host an event for the Queen and President Higgins to celebrate the arts and culture across the island.
There has been speculation since the Queen's momentous visit to Ireland in May last year that a senior Sinn Fein figure would meet her at an event.
Mr McGuinness, a former IRA commander, was always the candidate to shake the Queen's hand but delicate talks have been going on for months to arrange a suitable venue and occasion. Sinn Fein have stressed the meeting is not a celebration of the Jubilee.
Mr Adams defended the decision, saying: "We don't have to do it. We're doing it because it's the right thing to do, despite the fact that it will cause difficulties for our own folk. But it's good for Ireland. It's good for this process we're trying to develop. It's the right time and the right reason. After Martin McGuinness completes this engagement he will be as true, as staunch, as active a republican as he ever was."
Mr Adams called for support for the meeting and handshake from republicans and nationalists and said it was a "symbolic and significant step". He urged people opposed to the move to protest peacefully.