These were "exciting and hopeful times" for Ireland, the Taoiseach, Mr Ahern, said at the close of his week-long visit to the US.
Economically there had been "huge strides forward", and peace was "bedding down" in Northern Ireland.
Mr Ahern was speaking at Fairfield University, a Jesuit institution in Connecticut, where he received an honorary doctor of laws degree and delivered a lecture entitled: "Ireland Today: Building on Peace".
In his lecture he paid tribute to the "key role" played by US companies in the economic "transformation" of Ireland. He also acknowledged "the enormous contribution that the US has made thus far in supporting the peace process".
He asked the US to continue encouraging the parties in Northern Ireland "to make the final steps towards full implementation of the Good Friday agreement".
Much of the tension had gone from the marching season, which was the quietest for many years.
"Peace is bedding down," he said. This was due in part to the "architecture" of the agreement which provided the means for those from differing traditions to work together on the practical matters of running a society.
"A further, less tangible factor, is the sheer length of time that has now elapsed since the first ceasefires - going on 10 years. This has helped increase and deepen confidence that the new era is for real and here to stay."
He continued: "The IRA, with the encouragement of Sinn Féin, must make clear in unequivocal terms that paramilitary activity is at an end and will not be resumed, and do so in a way that convinces unionists and the rest of us that this is the case.
"Unionists must be able to reassure nationalists that once this is done, they will resume participation in the institutions in a full and sustained way. Time is short and we must all act soon to get politics back on track.
"I have made clear elsewhere that I believe elections at an early date in Northern Ireland are a key part of the way forward.
"It has been five years now since the last time the people have spoken in Northern Ireland. It is time for them to have their say again."