Gordon Brown and Bertie Ahern have urged Northern Ireland's parties to complete the process of devolution by taking on policing and justice powers.
The premiers were in Manchester for Munich commemorations
The St Andrews Agreement set a May deadline, but some DUP members remain to be convinced.
The premiers said the implementation of St Andrews was "building the community confidence necessary to enable transfer of these powers to take place".
They were in Manchester to mark 50 years since the Munich air disaster.
Last May, devolution was restored to Northern Ireland after the DUP agreed to share power with Sinn Fein, but Westminster still retains control over policing and justice powers.
Sinn Fein have identified the transfer of these powers as a major priority.
However, DUP deputy leader Peter Robinson said on Sunday they had never signed up to the May deadline "or any other arbitrary date set by the government".
Mr Robinson said his party first needed to be "satisfied beyond doubt that there is the necessary confidence and support within the community" for such a move.
"While Mr Brown and Mr Ahern may feel the 'time is right,' we do not hold to such a view while the IRA Army Council still exists, neither the funding package nor modalities are agreed and other issues remain unresolved," he said.
In their joint statement, the British and Irish prime ministers said: "We stand ready to help the political parties as they work to complete the process of devolution through the devolution of policing and justice powers."
They added: "Having seen the huge progress made, we are convinced that the time is right for the parties to move forward and take the final steps towards full devolution and full normality."
It was the third time the pair have met since Mr Brown became prime minister in June.
Both leaders also confirmed they would attend the Northern Ireland Investment Conference in Belfast in May, which they described as an opportunity "to demonstrate to the world that the peace and stability it now enjoys is here to stay".
They praised Northern Ireland's politicians for "putting the case for greater investment at the highest levels in the United States and in Europe".
"We have seen the smooth running of the North-South and British-Irish Institutions, delivering tangible benefits both on the island of Ireland and across these islands.
"It is therefore with genuine confidence that we look forward to the continued success of these institutions."
They added: "These are enormously hopeful and positive days for the people of Northern Ireland.
"Our two governments remain fully committed to working closely together in partnership for the benefit of Northern Ireland and of all of the people of our two countries."