"More than 100 journalists around the world are being persecuted in similar fashion using strong laws that shouldn't be used at all, so I think it's a very important to go back and defend our case," Mr Morison, 66, said before flying from Melbourne on Friday.

"We must face this in the interests of a free media in Thailand," he said.

Mr Morison, a former senior editor of The Age, and his Thai colleague Chutima Sidasathian, will face trial in July on charges of criminal defamation and computer crimes brought against them by the Royal Thai Navy.

The charges relate to their crusading and award-winning coverage of Myanmar's Rohingya Muslim minority, who have been described by the United Nations as among the world's most persecuted people.

The Thai navy took action over one paragraph from a Reuters news agency report that was re-published in Mr Morison's Phuketwan online service that he operates on the Thai resort island of Phuket.

The navy has inexplicably taken no action against Reuters which won a Pulitzer prize over investigative stories on the Rohingya which included the paragraph.

The case highlights Thailand's increasing use of restrictive defamation and computer crime laws to silence critics and has been condemned by the United Nations and media and human rights groups.

The US State Department has referred to it in its annual report on people trafficking, a sensitive issue in Thailand.

Mr Morison said he and Ms Chutima had done nothing wrong and therefore could not see how they could apologise.

"We are relying on the Thai justice system to exonerate us," he said.

"We see this as an unfortunate, misguided attempt by someone with a vendetta against Phuketwan to silence us," he said.

But Mr Morison and Ms Chutima appear to be facing a perilous situation.

Thai authorities last November declared them guilty in a ruling on an application for the government to pay the cost of their bail.

Thailand's military junta that toppled a democratically-elected government last May, after months of political upheaval, has moved swiftly to stifle dissent.

Hundreds of dissenters have been taken to military bases for so-called "re-education."

High-level diplomatic efforts to try to get the navy to drop the case against Mr Morison and Ms Chutima have so far failed.

After initially refusing to allow Mr Morison to return to Australia to see his 91-year-old father, who is unwell, Thai authorities granted him leave to travel to Australia over the new year with an order he return his passport to a Phuket court by February 8.

A wave of prosecutions have been launched in Thailand that appear designed to mute journalists and activists speaking out about corruption and human rights abuses.

Veteran British investigative journalist Andrew Drummond has quit Thailand after 25 years, saying his patience and financial resources had been exhausted after fighting defamation charges, many of them by foreign criminals living in Thailand.

Andy Hall, a British rights activist, is facing possible jail and substantial fines for writing a report for a Finnish non-government-organisation detailing alleged abuses in the Thai fishing industry.