On Friday the second of these investments of time finally bore fruit. For a man whose opinion-poll ratings have barely dipped since the general election, Friday's historic agreement is like icing on the cake. Whatever problems are to be overcome if the political settlement is to become a peace deal, Mr Blair is likely to benefit for getting this far. His work may, indeed, be recognised when the Nobel peace prize is awarded.
"Blairism" is already a model among left-wing European parties, and Mr Blair's reputation will be boosted further afield, including in the United States. He may not enjoy the public recognition of Baroness Thatcher, but among Washington's political elite the British premier is a rising stock. Being seen on the international stage can only boost the image of Blair as a statesman. There will be reflected glory from further meetings with President Clinton when he (almost certainly) returns to visit Northern Ireland in six weeks' time.
In the less exalted world of domestic politics, the political settlement will have benefits, too. Northern Ireland has dominated the news to the exclusion of almost everything else. Mr Blair's decisive intervention contrasts with the lacklustre and directionless Conservative leadership. It also moves the focus away from the problems the government has encountered, from Bernie Ecclestone to welfare reform.
More important is the fact that, one year into his premiership, Mr Blair can already claim a large, concrete political achievement. For an administration often accused of an obsession with style and soundbites rather than substance, this is a huge bonus. The Prime Minister's central role in the negotiations proves he is a serious politician dedicated to something more than winning elections.
It also shows him in another, less familiar light, that of the accomplished political practitioner rather than the public communicator. One of John Major's most convincing political assets was his ability to master detail and to emerge victorious from complex negotiations. It was those skills that served him well both in the Maastricht treaty talks as well as the drafting of the Downing Street Declaration and Joint Framework Document. Now Mr Blair has proved that he, too, can close a deal with the best of them.
But the Prime Minister should be wary of resting on his laurels. Much of his hard work could be undone if, as is possible in the coming months, the deal comes apart. The settlement has come early in the parliament and will be far from the minds of voters when they next go to the polls.
Moreover the British public has become inured to the Northern Ireland situation - good or bad - and appears to judge politicians on more mundane issues, such as the economy or sleaze, rather than progress towards peace. That, at any rate, was the harsh lesson delivered to Mr Blair's predecessor.