Martin Parkinson is due to give evidence before the Senate inquiry on Friday, which is also his final day as secretary of the Department of Prime Minister and Cabinet.

The Senate committee is looking at whether Mr Pyne and Ms Bishop breached ministerial standards by accepting controversial jobs soon after retiring from politics at the federal election in May.

Mr Pyne, the former defence minister, has picked up a defence-focused role with professional services giant EY.

Ms Bishop, the former foreign minister, has been appointed to the board of foreign aid firm Palladium.

In a report tabled in parliament in July, Mr Parkinson cleared the former ministers of breaking the guidelines over their post-politics jobs.

The standards state that ministers must not lobby or have business meetings with politicians or public servants within 18 months of leaving parliament, on matters they dealt with in their final 18 months in office.

In a very brief written submission to the inquiry, Palladium endorsed the ministerial rules.

"We strongly endorse the requirement for former ministers of state to adhere to all obligations concerning post-ministerial employment," Palladium chief executive Christopher Hirst wrote to the committee.

The inquiry is due to report by September 10.

Australian Associated Press