The general secretary of the GMB, Tim Roache, has resigned after suffering from ill health, the union has announced.
In a statement, the GMB said: "Tim has unfortunately been suffering with ill health for some time now and has made the difficult decision to stand down from his role, that he does not feel able to continue, in leading our union going forward.
"A meeting with the finance and general purposes committee will be convened to discuss the resignation and further updates will follow."
Mr Roache's resignation comes just months after he was re-elected as general secretary in November last year following a ballot of union members.
Under his leadership the GMB backed Lisa Nandy in the race to become Labour leader in January this year, with Mr Roache describing her as "a breath of fresh air".
Following the election of Sir Keir Starmer, Mr Roache called for the party to start a "new chapter", adding: "We need to leave behind the infighting and navel-gazing and get on with being a government in waiting."
