But the MP, sacked by May in July, said he had not yet met or discussed the agenda with the new Prime Minister, as he launched the Northern Powerhouse Partnership, a think-tank to drive the project forward and help push the agenda of greater powers and investment for the regions.
The new body, an independent group of politicians, business and civic leaders, which does not yet have an office, will be chaired by Osborne, who has recruited the former mayor of New York, billionaire businessman Michael Bloomberg, to advise the powerful new elected ''metro'' mayors being created in city regions including Manchester, Liverpool and Sheffield.
The future of the initiative, launched by Osborne in 2014, came under question after May's arrival in 10 Downing Street in July.
She initially appeared reluctant to use the phrase ''Northern Powerhouse'', speaking instead of a broader nationwide industrial strategy, rather than a regional focus solely on the north.
And senior Labour politicians in the north have recently spoken of Whitehall briefings casting doubt on the new Prime Minister's commitment to the agenda.
But at the launch of the new think-tank in Manchester today, Osborne said May's new administration and Sajid Javid MP, Secretary of State for Communities and Local Government, were now on-board with his ideas.
Osborne said: "They thought about the Northern Powerhouse but they have now committed to it, Theresa May has committed to it, Sajid Javid has committed to it, and across the Government, of course, people whose previous roles they had were also involved in building the Northern Powerhouse, so there's national Government helping.
"Of course the partnership with Government is important, but the Northern Powerhouse has to be owned by the north, run by the north, it's got to have enthusiasm in the north."
Osborne dismissed suggestions no meeting with the Prime Minister meant she was not committed to his agenda.
He said: "That's not actually, having spent six years in Downing Street myself, the way it works, which is, you know, you approach the relevant cabinet minister, which is Sajid Javid, and speak to him about it.
"And as you can see from the Government response today, he's been very positive."
Osborne told reporters, while he had not met Mrs May, northern civic leaders had met her "most senior adviser" last week and got the message that Number 10 were "100% committed to the Northern Powerhouse."
Earlier, Osborne said there was a "little bit of a wobble" about Number 10's commitment in the first days of the new Government, but suggested this had been overcome.
The former Tory chancellor and architect of "austerity" policies was defended at the launch by the Labour mayor of Liverpool, Joe Anderson.
Anderson said: "For me, I wouldn't have joined this panel if this was George Osborne standing up against the government and attacking the government, it's absolutely not the case.
"Theresa May has made a commitment to the Northern Powerhouse, there's a Northern Powerhouse minister, we've met, I've met the Northern Powerhouse minister, there's a commitment to Northern Powerhouse.
"To keep the momentum, sorry for using that word, the momentum going."
The Northern Powerhouse aims to devolve powers and money from Whitehall to northern city regions in a bid to boost their economic performance.
Plans included new investment in the north-south high-speed rail, HS2, described by Mr Osborne as "transformational" for the north, and an east-west version, HS3, linking the belt of northern cities from Liverpool to Hull, via Manchester and Leeds, which he described as "absolutely vital".
The plans also included the election of "metro" mayors for bigger city regions, including for Manchester, Liverpool and Sheffield.
Andy Burnham and Steve Rotheram, both MPs and Labour's candidates for the 2017 mayoral elections in Manchester and Liverpool, recently warned briefings in Whitehall suggested some proposals would be shelved.
But Sir Richard Leese, leader of Manchester City Council, concluded today's launch, saying: "Clearly this is not the last you have heard of the Northern Powerhouse. We are in this for the long haul."
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