More than 100 public service agencies are in the process of voting on enterprise agreements which set a baseline of 18 weeks paid parental leave for both caregivers.

Parents who have already taken leave can still take the additional weeks if their child is under two, with the main public sector union eager to spread the word before time runs out.

Primary caregivers currently get a minimum of 12 weeks of paid parental leave.

Those conditions were set by the Maternity Leave Act - a piece of legislation which was considered groundbreaking when it was passed in 1973, but which is now labelled a "dinosaur" in the space.

While some agencies offer extra weeks on top of the baseline, all of the major agencies and departments - except Infrastructure - will receive at least two additional weeks.

But leave for secondary caregivers will improve substantially, with entitlements to increase gradually to 18 weeks by 2027.

Most major agencies - which generally offer the best conditions in the APS - only grant between two and four weeks.

The new entitlements will help women to excel, allowing partners to share home and caring responsibilities "more equally", the Community and Public Sector Union says.

"Previous paid parental leave schemes reinforced traditional gender roles and held women back from equal workforce participation, and the CPSU is proud to be putting an end to that," national secretary Melissa Donnelly said.

Public servants, like Anna Doukakis, will be able to use additional leave on top of what they were offered under old agreements.

This is because her son, Connor, is still under the age of two.

Ms Doukakis, a public servant at the Department of Workplace Relations and Employment, will use her extra four weeks to work part-time and cut down on caring costs for Connor.

"Having extra leave wouldn't have changed when I went back to work," said Ms Doukakis, who is also a delegate for the Community and Public Sector Union.

"My husband and I split the primary care before he went to daycare a few weeks ago, so I went back at around seven months and I would have done that regardless.

"But the really good thing with the extra leave for me is that it means that I'll be able to work a part-time pattern ... without needing to worry about the financial impacts or similar of doing it that way."

A statement of agreed conditions, released by the Public Service Commission, is explicit that parental leave can be used this way.

But Ms Donnelly says the union is conscious of the deadline to use up the leave, and is trying to spread the word.

"We are working to ensure that parents of children under two are aware of these changes as they have a limited period of time to access the additional leave," she said.

"The CPSU will be getting in touch with all agencies and departments, requesting that they inform eligible employees of their rights and provide support as they access them.

Sue Williamson, Associate Professor of Human Resource Management at UNSW Canberra, welcomed the overhaul, deeming current conditions "not fit for purpose".

"We know that the old Maternity Leave Act hadn't been updated, or reviewed, or amended for 50 years, and it was just a dinosaur, and not fit for purpose.

"This is a really positive development, and not only does it increase the provisions available to parents, it also sends a really strong message that paid parental leave is important."

Importantly, she said, the new agreements also strip out "archaic" qualifying periods for paid parental leave.

"It's a relatively simple step, that's a really important one, and could help alleviate financial pressures for parents and families."

A spokesperson for Public Service Minister Katy Gallagher said the government wants the APS "to be a great workplace to attract and keep hard-working employees".

"By offering public servants more parental leave and making it easier to access, employees will know the public service values them and their careers."

The Albanese government also offers paid parental leave of 20 weeks to Australians who meet certain work and income requirements - which most public servants would be eligible for in addition.

But the public service still trails the private sector - with firms such as Ernst&Young offering 26 weeks of paid leave to both partners.

The Minister's office did not say whether she would support further increases in leave in future bargaining rounds.