The APS review's head David Thodey has announced a high-powered international reference group will act as a "sounding board" for the independent panel, including the likes of former NSW premier Mike Baird and former New Zealand prime minister Bill English.
The reference group includes current and former senior public servants from the United Kingdom, Canada, Singapore and New Zealand as well as former cabinet ministers.
Former head of Treasury in the UK Lord Gus O'Donnell, former secretary to the Cabinet in Canada Janice Charette, former head of Singapore's civil service Peter Ong Boon Kwee and current New Zealand State Services Commissioner Peter Hughes make up the international public service contingent of the group.
Joining Mr English and Mr Baird representing MPs, former Labor foreign affairs and defence minister Stephen Smith and former Liberal communications minister Helen Coonan are also part of the group.
Former Treasury deputy secretary David Morgan is the only former Australian public servant on the reference group.
"This group has great experience and will be an important source of lessons learnt in Australia and around the world," Mr Thodey said in a statement.
The deadline for submissions to the review, set to be the biggest of its kind in 40 years, have also been extended until July 31, after previously being due to close this Friday.
"We look forward to more insights from public and private sector organisations, and the many Australians who engage with government services in day-to-day life," Mr Thodey said.
The review has already faced criticisms that it is rushed and lacked contemporary public service experience on the panel, which is largely made up of business leaders.
Minister Assisting the Prime Minister for the Public Service Kelly O'Dwyer welcomed the announcement.
“The inclusion of experienced public service leaders and politicians from across the Commonwealth will help the panel deliver practical and meaningful recommendations that position our public service for the future,” she said.
The minister also encouraged people to use the extended deadline to make a submission to the inquiry.
“For those in business, civil society and the general public who interact with government in their day-to-day lives, your input is important. The future of the public service will affect every single one of us," Ms O'Dwyer said.