Christine Blower has been elected unopposed as the new general secretary of the NUT.
Ms Blower, who has been the union's acting general secretary since the death of Steve Sinnott in April last year, was the only candidate with the necessary backing when nominations closed last Friday.
"I am very pleased and very proud to be the general secretary," she said. "I will work tirelessly to achieve the best possible outcomes for teachers, children and the education service."
Ms Blower, 58, said that reform of the school assessment regime would be high on her agenda over the next year. The NUT conference voted last month to ballot members on a boycott of primary school Sats in 2009.
She called for reform of school inspections and league tables and for more trust to be put in teachers. Ms Blower also drew attention to the union's campaign to end child poverty and improve the quality of early-years education.
It is understood that one other candidate had been attempting to canvass support for a leadership bid, but failed to win sufficient backing to force a contest.
Ms Blower, 58, was a teacher for 33 years, starting her career as a foreign languages teacher at Holland Park School, in west London, the first purpose-built comprehensive in the capital. She went on to become head of modern languages at St Edmunds Secondary School in Fulham and also taught at Quintin Kynaston in Westminster before working for Hammersmith and Fulham Council to support children with behavioural difficulties.
Ms Blower was regarded as a leading light of one of the union's left-wing factions that previous leaders often referred to as "Trots". But she has now won widespread backing in the more unified NUT created by Mr Sinnott.
She steered the union though its first national strike in 21 years last April, just weeks after Mr Sinnott's death. This was not the first time she had made national headlines. While president of the union in 1997, she removed the eldest of her two daughters from Sats as a mark of protest at the tests.
Ms Blower is a supporter of greater unity between the teaching unions and is already holding discussions about joint campaigning that can be carried out ahead of the general election, which has to be held by next May.