Christine Blower will step down as general secretary of the NUT teaching union in May next year, TES can reveal.
The leader of the teaching union will retire from the post after more than six years in charge.
Ms Blower, the first female general secretary of NUT, said it had been "a pleasure and a privilege" to hold the post of the classroom union.
She added: "I will continue to devote myself to all aspects of the Union’s work over the coming months."
The NUT’s National Executive will discuss arrangements for the succession at a meeting in the New Year.
Ms Blower was elected unopposed as general secretary in May 2009 after a year as acting general secretary.