The nut's decision to join forces with the country's biggest further education union will strengthen its power before the next general election, the people behind the new partnership have said.
A new agreement between the NUT and the University and College Union (UCU) means the two unions have a combined membership of almost half a million.
NUT bosses say their aim is still the creation of a single education union in England, but the NASUWT and others are resistant to working closely with them.
The National Association of Head Teachers (NAHT), which has collaborated with the NUT to campaign against Sats, described the new partnership as "innovative".
Each union will retain its constitution, administrative machinery and membership. There will be a joint liaison committee and the unions will attend each other's executive meetings.
Teachers who move to colleges or sixth forms will be represented by the UCU, and lecturers who move to schools will be represented by the NUT. The unions said the agreement was prompted by the increasing number of workers transferring between sectors.
Christine Blower, general secretary of the NUT, said: "We are delighted to be joining together at a time when it is vital to defend public services and public sector workers. Half a million education professionals standing up for the education service will be a force to be reckoned with."
Sally Hunt, general secretary of the UCU, said: "We will be working together to provide the best possible education experience for children, students and adult learners - and the best conditions for staff across the sectors."
The UCU balloted its members and supported the NUT when it went out on strike last year. The NUT previously had a more informal agreement with Natfhe before that union merged with the Association of University Teachers three years ago to form the UCU.
John Dixon, head of the NUT's organising and membership department, said: "We see no need for competition between unions, and we want to ensure people who move sectors are still represented. There needs to be one voice for education from the cradle to the grave. And we will work closely, especially in areas where we overlap - for example the 14-19 reforms.
"We are always willing to speak to our sister unions. Far more unites us than divides."