George Osborne is set to earn £650,000 a year working just four days a month as an adviser for a US asset management fund.
It is almost nine times the £74,000-a-year salary he earns as a backbench MP.
Mr Osborne said he had consulted the Advisory Committee on Business Appointments which vets new jobs taken by senior former ministers, on the appointment.
He has already registered more than £780,000 in payments which he has received for 14 speeches which he has made since last September.
They include five made in the United States, one in Dubai and one in Antwerp.
Mr Osborne, who was sacked by Theresa May after she became Prime Minister last June, said he would be donating a £15,000 fee for a speech last month to Lloyds Bank International to charity in his Tatton constituency in Cheshire.