David McBride leaked classified documents to the ABC and is facing charges of theft of commonwealth property, breaching the Defence Act and unauthorised disclosure of information.

Mr Xenophon says it's a privilege to act for McBride, who is due to stand trial in the ACT Supreme Court in September.

"The latest accusations of war crimes in Afghanistan on Four Corners reveal the very issues that McBride was trying desperately to advise military commanders and politicians of in 2013," he said.

"His will be a test case for whistleblowers and the right for all of us to know what happens in the shadows of our government and military."

Mr Xenophon runs a law firm with former journalist Mark Davis, who says they will need to get clearance to see the accusations against McBride.

McBride was initially representing himself in court but recently began an online fundraiser to beef up his legal team.

The 55-year-old leaked classified documents to ABC journalists in 2017, who went on to produce a series called The Afghan Files.

The reports aired allegations of Australian soldiers carrying out unlawful killings in Afghanistan.

The two journalists involved are also being pursued by federal police for publishing the documents.

Australian Associated Press