A 73-hour strike was due to begin at 7am on Monday (20 October) at Blackpool Victoria, Clifton and Fleetwood hospitals.
The workers had been carrying out tasks – such as taking blood, performing electrocardiogram tests and inserting cannulas – that should have been paid at a higher hourly rate.
Before a previous 48-hour walkout in September, the trust accepted the healthcare assistants were performing extra duties above their role and agreed to provide them with back pay.
To avert Monday's strike action, the trust has now agreed to drop plans to withhold some of the money owed to staff.
Following Unison's campaign, the 700 workers will now work at a higher pay band, and the union estimates they will be awarded more than £6m in back pay.
Unison North West regional organiser, Sam Doherty, said: ‘This is an amazing victory for the healthcare assistants in Blackpool, putting millions of pounds into the pockets of some of Blackpool's lowest-paid NHS workers.
‘Despite the trust's initial refusal to pay them what they were owed, the staff stood together, took strike action and won.
‘This is a huge victory, but the campaign won't end until we've ironed out the final details.
‘The trust needs to guarantee everybody is included and that deal is implemented fairly and swiftly.'
In response, Maggie Oldham, chief executive of Blackpool Teaching Hospitals, said: ‘We are grateful to our health care assistants for the important role they play in supporting patients across our hospitals and services.
‘I'd like to thank them and our colleagues at Unison for their commitment to resolving this issue. We are working hard to ensure that colleagues receive their additional pay as quickly as possible.'