The approval for the transfer of policing and justice powers from London to Belfast was achieved by a vote of 88-13 in the Northern Ireland Assembly, with only one party opposing the move.
The First Minister Peter Robinson said: "Throughout history there are times of challenge and defining moments. This is such a time. This is such a moment."
The breakthrough was the culmination of years of effort by the British Government, Dublin, Washington and local parties. But some of the shine was taken off the achievement by the fact that the vote, though decisive, was not unanimous and was preceded by days of political rancour.
At one point it had been widely assumed that the issue would go through on the nod, providing a much-needed display of unity for a coalition administration which has had many disagreements within its ranks.
Instead the Ulster Unionist Party (UUP), which holds the Health portfolio and is the the third largest party in the Assembly, argued that the time was not right for the transfer. It accused the two dominant parties, Sinn Fein and Peter Robinson's Democratic Unionists, of operating "a two-party political carve-up".
The UUP, in uncharacteristically assertive mood, complained that a meeting with Deputy First Minister Martin McGuinness had ended abruptly after less than five minutes when he "showed us the door".
The party had hoped to win concessions which included changes in education policy and an enhanced role for itself, saying it was not in principle opposed to policing devolution.
The UUP attracted little support for its stance, instead coming under huge pressure from sources which included both the government and the Conservative party, with which it has formed an electoral pact. It was pressed not just by the Obama administration but also, highly unusually, by George W Bush, who in a rare intervention called on David Cameron to persuade his allies to support devolution.
Mr Cameron said the former president had stressed it was crucial for everyone to back devolution but added: "The one thing we cannot do is force people to vote a particular way. We have played a thoroughly constructive role, very, very supportive of what the Government wants to do and what we all want to do, which is to see devolution work properly."
Kate Carroll, whose police officer husband Stephen was shot dead by dissident republicans exactly a year ago, telephoned the BBC with an emotional appeal. "Please, please, please stop this arguing and fighting over something that we know is going to move on anyway," she said. "Please let it move on. Who gets on, fighting like children in a playground? We want to speak for ourselves, we want to rule ourselves. Just get up and get on with it."
UUP leader Sir Reg Empey, defending his party's vote, said he was pledged to making power-sharing work. But he insisted: "We exercise our rights refusing to bow to the blackmail and bullying to which we have been subjected in recent weeks."
In the coming months, Belfast will be given more power with a new minister, who is expected to be David Ford of Alliance party, gaining oversight of policing and justice matters. Chief Constable Matt Baggott will retain operational control of the Police Service of Northern Ireland, with intelligence matters continuing to be the preserve of his Special Branch and MI5.
The Tory alliance: Cameron's connections
Q: How has David Cameron been dragged into the dispute?
A: Last year the Tories negotiated an electoral alliance in Northern Ireland with the Ulster Unionist Party (UUP). They are preparing to field joint candidates in the province's 18 constituencies in the general election expected on 6 May.
Q: Why did the Tories enter into the alliance?
A: The UUP have long been natural allies of the Tories, who once routinely described themselves as the Conservative and Unionist Party. Sceptics suggest it was aimed at bolstering a narrow Tory majority.
Q: What about the Ulster Unionists?
A: Once the dominant voice, they have been eclipsed by the Democratic Unionist Party (DUP). Ten years ago there were 10 Ulster Unionist MPs; today they have just one in the Commons.
Q: What influence does Mr Cameron have over his partners?
A: Almost none. Not even the intervention of former President George W Bush made any difference. Mr Cameron made little attempt yesterday to disguise his frustration with their stance, insisting that the Tories had done "everything we can".
Nigel Morris
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