The High Court has dismissed an appeal by some of Australia's biggest media outlets including The Sydney Morning Herald and The Australian, finding they are the publishers of third-party comments on their Facebook pages.

Former Northern Territory detainee Dylan Voller wants to sue the companies in the New South Wales Supreme Court over alleged defamatory comments on their Facebook pages.

But the case had been stalled by a dispute over whether the outlets were the publishers of the material.

The High Court today found that, by running the Facebook pages, the media groups participated in communicating any defamatory material posted by third parties and were therefore responsible for the comments.

Dylan Voller clear to continue defamation case

Today's decision cleared the way for Mr Voller to continue his defamation case against some of Australia's biggest media companies.

Mr Voller's treatment as a detainee sparked a royal commission into the Northern Territory's youth detention system, after images of him shackled to a chair wearing a spit hood were revealed by the ABC's Four Corners program.

He launched the defamation action in the New South Wales Supreme Court against groups including The Sydney Morning Herald, The Australian and Sky News, over third-party comments about him on their Facebook pages.

But the case was sidetracked when the debate arose about whether the media companies were the publishers of the comments in question.

Today, the High Court rejected the argument that, to be a publisher, an outlet must know of the relevant defamatory matter and intend to convey it.

The court found that, by creating a public Facebook page and posting content, the outlets had facilitated, encouraged and thereby assisted the publication of comments from third-party Facebook users, and they were, therefore, publishers of those comments.

'Historic step forward', Voller's lawyers say

There has not yet been a ruling on whether or not the comments are defamatory and the publishers do have other defences they can rely upon.

But lawyers for Mr Voller said their client was pleased with today's outcome and has a sense of vindication.

In a statement, his legal team also welcomed the ruling for its wider implications.

"This decision put responsibility where it should be; on media companies with huge resources, to monitor public comments in circumstances where they know there is a strong likelihood of an individual being defamed:"

Lawyers for the media groups had argues in the High Court that they might have facilitated the process, but they were not the publishers of the material.

But lawyers for Mr Voller told the High Court that, under the law, communication of a defamatory comment did not have to be done intentionally.

"Any degree of participation in that process of communication, however minor, makes the participant a publisher," the lawyers' submissions said.

One of the difficulties for the media groups at the time was that Facebook did not allow them to turn off the comments function.

That has now changed.

Mr Voller had not suggested any of the media outlets failed to remove the comments once they became aware of them.

In a statement, a Nine spokesperson said the media giant was disappointed with the decision.

"Nine recognises the decision of the High Court which makes news businesses liable for any post made by the general public on their social media pages as the "publisher" of those comments," the spokesperson said.

"We are obviously disappointed with the outcome of that decision, as it will have ramifications for what we can post on social media in the future.

"We are hopeful that stage two of the review of the Model Defamation Provisions will take account of the High Court's decision and the consequences of that for publishers.

"We also note the positive steps which the likes of Facebook have taken since the Voller case first started, which now allow publishers to switch off comments on stories."