A joint DUP and Sinn Fein request that the NI Secretary vacate his offices at Stormont is evidence of the parties' "serious intent", Peter Hain said.
Peter Hain said Ian Paisley was now working with his "old foe"
In a letter signed by Ian Paisley and Martin McGuinness, he was asked to relocate to Stormont Castle before power sharing begins in early May.
It is thought to be the first letter jointly signed by Democratic Unionists and Sinn Fein politicians.
Mr Hain told Broadcasting House on BBC Radio 4 he would be delighted to leave.
"The two most polarised parties have done what they have never been willing to do before, to share power on 8 May, I believe it will stick," he said.
"Confirmation has come in a letter I have just received, the first one ever jointly signed by Ian Paisley and his old foe, Martin McGuinness, as first and deputy first ministers designate."
"I am pleased that the party leaderships are getting down to the business of preparing for government and, to that end, I have instructed my officials to make themselves available to assist with advice on policy and analysis so that the Executive is in the best position to operate effectively from day one, 8 May."
Devolved government is to return to Northern Ireland in May following an agreement between the DUP and Sinn Fein leaders.
On 26 March, Ian Paisley and Gerry Adams, sitting side by side for their first news conference in Stormont, confirmed that power-sharing would begin on 8 May.
Mr Paisley said the DUP was committed to full participation in government and Mr Adams said it was a "new era".
The British and Irish governments had said they would shut the assembly if an executive was not agreed.