Labour’s general secretary Iain McNicol is standing down to pursue new projects, the party has announced.
The former trade union official, who has served as the Labour Party’s most senior employee since 2011, said he was leaving to “pursue new challenges”.
He was appointed to the role under the party leadership of Ed Miliband, but has clashed with current leader Jeremy Corbyn and his allies.
It is understood that the left of the party has long hoped to replace him.
Mr Corbyn said: “I would like to personally thank Iain McNicol for his long and dedicated service to the Labour Party as general secretary.
“He has run our party’s organisation at a time of great change, including a near tripling of the membership, two general elections and the EU referendum.
“Iain has served the Labour Party and trade union movement in a wide range of roles throughout his career and is a credit to our movement.
“I am confident Iain will continue to play a major role in politics and our party, and will support our team inside and outside Parliament with his experience and skills.”
Mr McNicol will stand aside once a successor is chosen.
His successor will be confirmed at the party’s annual conference following a recommendation by the National Executive Committee (NEC).