Among secondary teachers, 57.5 per cent worked unpaid overtime, with an average of 12.5 extra hours.
Across all education staff, including teachers, teaching assistants, playground staff, cleaners and caretakers, 37.6 per cent worked unpaid overtime – a figure higher than that for any other sector.
Christine Blower, general secretary of the NUT teaching union, said the scale of teachers’ unpaid overtime was “untenable”.
“Much of teachers’ excessive workload is as a result of government education policies and initiatives, including the totally out-of-control accountability systems," she said.
“We already have a shortage of teachers in many subjects. Unless teachers’ working lives are improved significantly, the situation will only get worse, with many experienced teachers and graduates either leaving or not even considering entering the profession."
She added: “Working weekends and long into the evenings under such intense scrutiny and pressure is detrimental to the health, family and social life of teachers and is clearly bad for education.”
The TUC’s research has been published to mark “Work Your Proper Hours Day”, when the union urges staff to take a "proper lunch break" and to leave work on time.
The findings come just weeks after teachers inundated the Department for Education with tens of thousands of responses to its Workload Challenge, which was launched by education secretary Nicky Morgan and deputy prime minister Nick Clegg in October.
In response, the government announced a “new deal” in which teachers would no longer be subjected to major changes in Ofsted inspections or government policy during the academic year.
A spokesman for the Department for Education said: “It is no secret that we have made some very important changes in schools – changes that would not have been possible without the hard work and dedication of our teaching profession. As a result of their efforts, standards are now higher and a million more children are in good or outstanding schools.
“Our recent Workload Challenge had thousands of responses and helped to build a picture of the root causes of unnecessary workload. We want to support the profession to tackle these issues.
“We will monitor progress by tracking teacher workload through a large-scale, robust survey next spring and every two years from then and continue to develop ways to help teachers focus on what really matters – giving every child the very best start in life.”