Jonathan Powell, former chief of staff to Tony Blair, is to become a senior executive at a leading bank.
Mr Powell worked alongside Tony Blair for more than a decade
He will take up a full-time position as a senior managing director of Morgan Stanley's investment banking division.
Mr Powell left 10 Downing Street when Mr Blair stepped down as prime minister in June, having been one of his most trusted lieutenants for 12 years.
A former journalist and diplomat, Mr Powell is expected to start work in his new capacity next month.
While many government officials have gone on to work for banks in an advisory capacity, Mr Powell's role is more unusual in that it will be full time.
He is expected to play a role in transactions involving some of the bank's largest clients in UK and Europe.
In a statement, the 51-year old said Morgan Stanley's "reputation for innovation combined with its extensive global reach means there is a great opportunity to build and strengthen the bank's market-leading franchise."
Mr Powell is not the first member of Mr Blair's former inner circle to find lucrative work in the private sector.
Anji Hunter left her job as head of government relations in 2001 to work for oil giant BP.