Members of the Association of Teachers and Lecturers (ATL) voted overwhelmingly in favour of pushing forward with talks about forming a new union with the NUT this evening.
Following a long debate behind closed doors at its annual conference, where more than 20 members spoke about the idea, the more moderate union got behind the plans.
Mary Bousted, general secretary of the ATL, told journalists that a ballot of members is likey to take place next year.
The news comes after NUT members backed continuing talks over the matter at their annual conference over the Easter weekend.
Special conferences for both unions are expected to be held in the autumn to consider whether to ballot members over forming a single union.
Ahead of the debate, Peter Pendle, deputy general secretary of the ATL, warned that without change the union would become “less effective” in years to come, due to the current political environment and the “competitive world we live in”.
Following the vote, Dr Bousted stressed that one education union would be a "strong voice that will be able to fight more effectively".
But professional unity of all the teacher unions is a long way off as NASUWT wants to remain independent.
Earlier this month, the union's general secretary, Chris Keates, told TES that she would “respect the decision of sister trade unions” . But she said that it was “better” for ministers to receive six letters from unions on issues such as pay, rather than one with six signatures.