Former British Foreign Secretary David Miliband has confirmed that he is to step down as an MP.
Mr Miliband said he had accepted the position of president and chief executive of the International Rescue Committee in New York.
In a letter to his constituency party chairman in South Shields, he said it was "very difficult" for him to be leaving politics in the UK.
He said that he still "passionately" wanted to see Labour returned to power and he praised the leadership of his brother Ed, who defeated him for the party leadership in 2010.
"After the leadership election, I felt I could be most helpful to the party on the frontline, in South Shields and around the country, rather than on the front bench in parliament," he said.
"I felt this gave Ed the space and at the same time the support he needed to lead the party without distraction.
"He has done so with real success, leading a united team that has taken the fight to the Tories.
"I am very pleased and proud that our shared goal of making this a one-term government is achievable."
Ed Miliband said that British politics will be "a poorer place" without his brother.