David Miliband will resign as an MP to take up a job in America, a move which is set to be announced today.
The former foreign secretary has been offered a job running the International Rescue charity in New York.
Shadow Chancellor Ed Balls has said “we'll all miss him in Parliament" while David Lammy tweeted: “David Miliband a big loss to PLP [Parliamentary Labour Party].”
David Miliband has been a backbencher since losing the Labour leadership contest in 2010, something that shocked many people at the time because he was so widely considered to be one of the party's high-flyers - he was one of the youngest foreign secretaries Britain has ever had.
A by-election in South Shields shouldn't cause the Labour party too many problems - Miliband had a massive 18,995 majority.
There were many who saw him as the possible successor to his brother, Ed; to many he was a standard bearer of Blairite ideas and the right of the Labour party.
Tory MPs have seized on the announcement to accuse Labour of “lurching to the left”.
Ex-cabinet minister Lord Mandelson said: "Never say never. I wouldn't say goodbye to David Miliband forever in British politics."