Dr Donaghue was first appointed in late 2016 and since then has served as the second law officer of the Commonwealth in High Court cases relating to public servant free speech and the section 44 citizenship saga.

Senator Cash on Friday said Dr Donaghue had served ably as solicitor-general, both appearing before the courts in significant litigation and providing trusted advice on government policies.

"He has also played an active role in identifying, raising and managing matters of whole-of-government legal risk, including through his role on the Significant Legal Issues Committee," she said in a written statement.

Former Coalition government attorney-general George Brandis appointed Dr Donaghue as solicitor-general following the resignation of Justin Gleeson from the role.

Dr Donaghue represented the Commonwealth in a High Court case relating to the sacking of former Immigration Department employee Michaela Banerji over tweets that criticised the federal government.

The nation's highest court found the federal government's limits on free speech in the public service were constitutional, clearing the way for punishments targeting bureaucrats who expressed political views.

Before becoming solicitor-general, Dr Donaghue was counsel assisting the Royal Commission into the Building and Construction Industry and was counsel for ASIO in the case of Mohammad Haneef.

He was appointed Senior Counsel in 2011 and Queen's Counsel in 2014.

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