Paramedics in NSW will receive a major pay boost after months of negotiations finally led to a deal between union representatives and the state government.

Following a series of late-night talks, the government and Health Services Union announced on Wednesday they had struck a deal for an average pay rise of 25 per cent across four years.

The deal recognises the changing role of paramedics in recent decades, from acting primarily as ambulance drivers, to performing increasingly complex medical interventions.

The bitter dispute has plagued the Minns government for more than eight months as paramedics pointed to higher salaries offered to their colleagues in the ACT, Queensland and Victoria.

Increases will range from 11 to 29 per cent, depending on paramedics' level of experience.

A first-year paramedic's pay will go from $74,363 today to $89,876 a year, while the base salary for a sixth-year paramedic will increase from $79,737 to $103,361.

A critical care paramedic in their second year, whose scope goes beyond that of general paramedics, will see their salary increase from $98,391 to $127,261.

Pay rises over the four year deal will be front-loaded, with three-quarters delivered in the first two years, to have NSW paramedics quickly catch up to their interstate counterparts.

The agreement will cost about $500 million, part of which is to be funded through savings from within the health portfolio, the government said.

HSU NSW secretary Gerard Hayes said paramedics had fought for proper professional recognition and "salary justice".

"Our paramedics are highly skilled professionals who exercise fine clinical judgement under incredible stress," he said.

"At the end of the day, the people that go in the back of that ambulance either live or die.

"Their work saves lives.

"Finally they will be paid for it."

The deal needs to be confirmed by the Industrial Relations Commission, where the parties entered mediation on Monday.

Paramedic Tess Oxley said the pay increase will change how frontline workers perform their jobs for the community of NSW.

"They know that when they need us and they call we'll be turning up and we will be proud and happy to be doing our job again," she said.

"I'm so proud of every single paramedic.

"Risking their registration was a massive leap, but that's how important this was."

Both sides wanted to avoid a catastrophic breakdown in services after thousands of union members vowed to allow their paramedic registrations to lapse from January 1 next year.

Health Minister Ryan Park called the increase a once-in-a-generation agreement, and said the case of paramedics was unique due to their changing roles and resulting pay disparity.

"This goes to the heart of what we're trying to do as a Labor Government, and that is deliver the benefits to our frontline essential workers," he said.

The opposition called on the government and Premier Chris Minns to reveal exactly where the money will come from to cover the pay increases and guarantee no reductions in budgeted frontline services.

"We acknowledge and applaud the hard work and dedication of NSW paramedics," an opposition statement said.

"However, the Minns Government should not be robbing our health system to pay the paramedics."