Greste, who has been jailed in Egypt for a little more than a year, had his conviction overturned in an Egyptian appeals court on Thursday.

But the Court of Cassation ordered a retrial, which meant Greste and his two Al-Jazeera colleagues would remain behind bars until it was held.

Speaking in Brisbane on Friday, his brothers, Andrew and Mike Greste, said the struggle would not be over until their brother was free.

"We view this decision as a positive step in the legal process and one step closer to justice being served," Andrew Greste said.

"The decision is also an acknowledgement that the first court trial was flawed and produced a number of procedural errors."

Peter Greste's legal team had already lodged an application to have the then-convicted criminal deported under a presidential decree issued in November.

According to the Egyptian state news agency MENA, the decree allowed the president, Abdel Fattah al-Sisi, to "surrender and transport non-Egyptian convicts and suspects to their countries to be tried or have their punishment implemented".

If Mr Sisi decided not to deport Greste and fellow Al-Jazeera journalist, Egyptian-Canadian Mohamed Fahmy, they will be forced to await a retrial.

The third Al-Jazeera journalist imprisoned in Cairo, Egyptian Baher Mohamed, would not be eligible for deportation.

The trio was convicted on charges they colluded with a terrorist organisation – the Muslim Brotherhood, which won democratic elections after the fall of former president Hosni Mubarek – to broadcast false news and tarnish Egypt's reputation.

Andrew Greste said because Peter was now "an accused person" rather than a convicted criminal, they would amend their deportation appeal accordingly.

"We believe that there is now a window of opportunity for the Egyptian president to exercise his presidential power under the decree," he said.

Mr Sisi has already said the original trial, which was almost universally decried as farcical, had reflected badly on his nation and he would have preferred they were deported rather than charged.

Because the decision to deport would essentially be a political one, Mike Greste said the public campaign to have his brother freed was invaluable.

"I don't think it can be overestimated the value that social media and public pressure has had on this case," he said.

"I think it has contributed enormously to where we are today and I think it has a terrific and tremendous affect on any future negotiations."

What was not clear was whether Peter Greste, as an accused man, would be required to make any admissions to secure deportation.

"(The decree is) literally one sentence and there's no regulation, there's no precedent and there's no formal prisoner exchange program between Egypt and Australia, so it's something that's going to have to be worked out," Andrew Greste said.

On the same issue, Mike Greste said: "We have made some attempts to try to have the decree defined and get a better understanding of what it exactly means, but we're yet to have any answers to those questions."

Foreign Minister Julie Bishop appeared confident last week that Peter Greste's release was imminent, although she dampened expectations a few days later.

"This is something we've come to expect in this case, in as much as the communication out of Egypt is sometimes mixed and confusing," Mike Greste said.

"So we didn't take too much stock in Julie Bishop's comments.

"We were … always looking forward to the appeal case and didn't expect entirely that he would be released before then."