The former chancellor will chair a partners council overseeing Exor, the listed holding company of the Agnellis.
Companies owned by the £10.5bn family investment business include Fiat and Ferrari – and even Juventus football club.
John Elkann, head of the Italian family and chief executive of Exor, said the council will “explore new ways to collaborate with friends and partners”.
Since leaving Parliament in April 2017, Mr Osborne has also been appointed editor of the Evening Standard newspaper, become an adviser to the world’s largest fund manager Blackrock, and chaired the Northern Powerhouse Partnership.
He also holds a string of academic posts at Stanford Business School and the Hoover Institution.
Of his latest role, Mr Osborne said: “I am delighted to have been asked to chair this impressive panel of business leaders.
“I look forward to chairing discussions that I am sure will provide useful insights and ideas for Exor and its companies.”
Mr Elkann added: “George Osborne will bring his unique knowledge and viewpoint to the council’s work.”