A culture of long hours of unpaid overtime for junior doctors will need to change following a multimillion-dollar underpayment settlement, believed to be the biggest in Australian history.

More than 20,000 junior doctors could share in a $229.8 million settlement pending NSW Supreme Court approval for a class action against the state's health department.

The lead plaintiff, Amireh Fakhouri, said she believed the culture was changing to properly recognise the work of junior doctors following the long-running class action, which was filed in 2020.

"This was not about us asking for more money; it was simply about us being paid for the actual hours that we work," Dr Fakhouri said.

Health Minister Ryan Park said junior doctors had been marred by a past history of poor treatment that had become "almost like a rite of passage".

"I want to say to our junior medical staff, that that's not on," he said on Wednesday.

"That's not the culture I want in NSW Health, it's not the culture we want at the coalface at our hospitals and at our health facilities."

Maurice Blackburn principal Rebecca Gilsenan, whose legal firm is one of two behind the class action, said underpayment has been a problem in NSW hospitals for a long time and the "landmark" settlement was driving change.

"Never before has a wage underpayment class action settled in Australia of this size," she said.

If the court approves the settlement, doctors who register for a share will be assessed for eligibility later this year.

The claim covers current and former junior medical officers who worked in the NSW public health system between December 16, 2014 to March 21, 2024.

Mr Park said he believed his government had made "significant inroads" in fixing systemic cultural problems within the state's health services since coming into government in March 2023.

"I'm not saying we've fixed it but we've made a big dent," he said.

The entire health system would need to be overhauled, including improving the culture among staff, hospital management and other leadership, Mr Park said.

NSW Health said changes had been made to internal systems to allow junior doctors to electronically claim overtime and call-back hours worked, as well as missed meal breaks.

The agreed settlement sum included legal costs and fees for distributing the settlement, the health agency said.

Those deductions mean eligible doctors will likely share in a significantly smaller sum than the near-$230 million settlement.

NSW nurses and midwives have also called a rally on Wednesday outside the Hawkesbury District Health Service, in Sydney's northwest.

They claim they have been told accrued leave will not be transferred when the facility becomes government-operated in July.