Two Australian lawyers banned from entering Papua New Guinea after preparing to represent authorities in a corruption case against that nation's prime minister have had their travel bans lifted.

The Australians, Queensland barrister Greg Egan and his junior counsel Terence Lambert, are now free to rejoin the case after the PNG National Court of Justice upheld their appeal against the bans.

It's been a tumultuous month in PNG politics, with the government moving this week to suspend Chief Magistrate Nerrie Eliakim, who last year issued an arrest warrant against Prime Minister Peter O'Neill for corruption charges, after an investigation by police and anti-corruption agency Taskforce Sweep.

At the time, Mr O'Neill responded by sacking the country's Attorney-General and others.

Last week, Fairfax revealed Mr Egan and Mr Lambert would fight their travel ban, arguing it is "a ploy" to further undermine the case against Mr O'Neill.

Australia's Department of Foreign Affairs and Trade refused to intervene, saying the case is "a private legal matter" between the men and the PNG government, and Australia "must respect PNG legal processes".

However a spokesperson for the department said on Wednesday the Australian High Commission in Port Moresby was continuing to make enquiries about the ban.

A letter signed by PNG's Chief Migration Officer Mataio Rabura​ on September 8, seen by Fairfax Media, instructed international airlines not to carry the men on any flights due to land in PNG, or risk penalties.

Australian and PNG legal bodies raised concerns over the travel bans, saying they could be viewed as an attempt to pervert the course of justice.

The PNG National Court of Justice agreed, ruling on Thursday that the bans were invalid.

Mr Egan, who has been practising law in PNG since 1988, and Mr Lambert referred the matter to the Department of Foreign Affairs and Trade in the hope it could be resolved at a diplomatic level.

But with no progress on that front, they last week lodged papers with the PNG National Court of Justice for a judicial review of the case.