Bertie Ahern, the Irish Premier, and Tony Blair, the outgoing British prime minister who has made plain his intention to include the resolution of the Northern Ireland conflict as part of his political legacy, were at Stormont castle to witness the swearing-in of the new ministers.
"This is a very important day for the people of Northern Ireland," said Blair. "But also for the people and the history of these islands. And in a sense, everything we've done over the last ten years has been a preparation for this moment."
Postions in the new government were filled based on how many seats each party holds in the Northern Ireland Assembly.
The Protestant DUP took up five posts while the Catholic Sinn Fein took up four. The Protestant Ulster Unionists took two positions and the Catholic Social Democratic and Labour Party took one.
|Martin McGuinness, a Sinn Fein leader, was|
sworn in as deputy first minister [AFP]
Spanning three decades, the conflict in Northern Ireland has claimed about 3,000 lives as the province's Protestant majority, who were largely in favour of remaining part of the UK, fought the Catholic minority who wanted a united Ireland.
With the British Army between them, the two sides often fought street by street.
McGuinness was himself once convicted of terrorism.
But in March this year, Paisley and Gerry Adams, the president of Sinn Fein, leaders of parties that had previously refused to co-operate with each other, agreed to share power.
"There are still many difficulties to be faced but let us be clear, the basis of the agreement between Sinn Fein and the DUP follows Ian Paisley's unequivocal and welcome commitment to support and participate fully in the political institutions on May the eighth," Adams said, after the agreement was reached.
Brendan O'Duffy, a professor at Queen Mary University of London, told Al Jazeera: "It's a question of two communities who mainly live apart but are learning slowly to get along with each other and respect each other's rights.
He called it a "transitional phase", saying: "It does still feel like a divided place. But since there is this core agreement on political means, I think gradually that will improve."
Both sides of the conflict have agreed to disarm and Tuesday's swearing in of Northern Ireland's first and deputy ministers marks the transfer of power from London to Belfast, with Northern Ireland now to run its own affairs.