It is run by former BBC and The Times executive James Harding, and former US ambassador to the UK Matthew Barzun.
The company has a number of high-profile backers, including tech investor Saul Klein and Nando’s executive Leslie Perlman, and promises to invest £25m in the paper.
Speaking after the sale was announced, Harding said he was “honoured and excited at the prospect of working together to renew the Observer”.
He added that he promises its readers “we will do all we can to live up to its history as a defender of human dignity and to give it a new lease of life as a powerful, progressive voice in the world”.
Journalists at the Guardian and the Observer went on strike on Wednesday and Thursday, concerned with what would happen to the newspaper in the hands of a new owner.
National Union of Journalists general secretary-elect, Laura Davison, said the 233-year-old newspaper “holds a unique and important place in public life and our members care about the next chapter in its history”.
Katharine Viner, editor-in-chief of Guardian News and Media, said: “I recognise how unsettling this period has been for Observer staff but we’re confident we have agreed the best possible way forward for the title’s journalists, its readers and the future of both the Observer and the Guardian.
“It is a model that will see investment in journalism and journalists, enshrines the Scott Trust’s values in the Observer’s future, and protects the Observer and Guardian’s ability to continue to produce trusted, liberal journalism.”