Chris Keates is to stand down as general secretary of the NASUWT union after 15 years at the helm.
Ms Keates was elected as the teaching union's first female general secretary in 2004, and was re-elected unopposed by the membership in 2009 and 2014.
Dave Kitchen, the NASUWT national president, said: “After 15 years as NASUWT general secretary, and far longer as an NASUWT member of staff and union activist, Chris Keates has advised the national executive of her retirement plans and that she will not be standing again for re-election.
“The process of electing her successor has started and pending the outcome of that process, and in the interim, Chris remains in post, so for the present it is business as usual.
“At the appropriate time, tribute will be paid to Chris for the work she has done and her years of service to the NASUWT and its members. Consequently, no further statements will be made at this time.”
Ms Keates joined the staff of the NASUWT in 1998 in a senior role with responsibility for policy co-ordination and development, and was appointed as NASUWT deputy general secretary in 2001.
She taught history and humanities in Birmingham secondary schools from 1971 to 1994.