Tony Blair is taking a part-time post with one of the best-known American banks on an estimated salary of more than £500,000 a year.
The former prime minister's first City job will be to provide JP Morgan with strategic and political advice. Mr Blair, who is not paid for his role as a Middle East envoy, said he expected to accept a "small handful" of similar posts in other sectors.
"I have always been interested in commerce and the impact of globalisation. Nowadays, the intersection between politics and the economy in different parts of the world, including the emerging markets, is very strong," he told the Financial Times.
Mr Blair, who stood down seven months ago, has already made a lucrative start on the international lecture tour. He was paid £250,000 for one appearance in China. He has also secured a £4.5m deal for his Downing Streetmemoirs.
Jamie Dimon, JP Morgan's chief executive, said: "There are only a handful of people in the world who have the knowledge and relationships that he has."
As well as his role in the Middle East, Mr Blair is also being backed as a possible president of the European Union by the French president Nicolas Sarkozy.