Former Irish Republican Army commander and current deputy first minister of Northern Ireland, Martin McGuinness, will meet Queen Elizabeth this week, marking a milestone in the province's peace process.
The Queen has never met a senior figure in the IRA or its political wing Sinn Fein.
Mr McGuinness will meet the Queen on Wednesday during a two-day visit to Northern Ireland as part of her Diamond Jubilee celebrations.
"Today's decision is the right thing to do, at the right time and for the right reasons," said Sinn Fein president Gerry Adams.
The IRA ended its campaign against British rule in 1998. The organisation killed the Queen's uncle Lord Mountbatten in 1979.