Jennie Formby is to stand down as the Labour Party’s most senior official.
She said it was the “right time” to make way as general secretary, with the party under new leadership following Sir Keir Starmer’s election last month.
The former Unite union officer said she had taken on the role in 2018 primarily to support then leader Jeremy Corbyn.
Mrs Formby, who was treated for breast cancer in 2019, said it had been a privilege to serve during what had been a “very challenging period”.
Sir Keir thanked Mrs Formby for her commitment and energy while deputy leader Angela Rayner said she had “blazed a trail” for women in the Labour movement.
Labour’s ruling body, the NEC, will meet soon to discuss a timetable to choose her successor.