The 32-year-old has spent more than 11 years in jail after being convicted of murder in 2009.

His father, Simon Palfreeman, spoke to him briefly overnight.

"He's very happy to be out of detention but I think still very stressed and tired about what's happening," Mr Palfreeman told ABC radio.

"Of course, even though he's out of detention, he's still being detained in Bulgaria."

Foreign Minister Marise Payne is also concerned he is being blocked from leaving the country.

"We call on the Bulgarian government to ensure Mr (Jock) Palfreeman receives due process, consistent with Bulgarian law," Senator Payne told AAP.

"Australia has provided and will continue to provide everything required to assist Mr Palfreeman's departure from Bulgaria as soon as possible."

Simon Palfreeman described the process to date as an "absolute rollercoaster".

"I wake up very early, turn my phone on, and something dramatic has happened," he said.

"This was happening during the court process 10 years ago, but it's also happening now."

Mr Palfreeman is hopeful - but not holding his breath - about seeing his son again soon.

"In 12 years, I'm not confident about anything with regards to the Bulgarian judicial system," he said.

"The Bulgarians are putting out roadblocks, illegal roadblocks, at every single turn."

For about three weeks, Bulgarian officials claimed Palfreeman did not have a passport and therefore could not leave the country.

However, police raided his cell overnight and confiscated his passport, saying they will only will give it back once he is allowed to leave Bulgaria.

Palfreeman's parole angered nationalist politicians in Bulgaria, prompting the chief prosecutor to ask for a review of the ruling by the country's highest court.

The court has two months to make a decision.

The 32-year-old has served 11 years of a 20-year sentence since being found guilty of murder and attempted murder in the stabbing of two Bulgarian youths, one of whom died, during a street melee in 2007.

Palfreeman said he was acting in self-defence.

"I know he didn't murder that boy and that's all that Jock and I need to know," Mr Palfreeman said.

"I know Jock regrets the fact that anybody had to die that night."

Speaking in Bulgarian to reporters after his release, Palfreeman said he would stay with friends and would not attempt to leave Bulgaria before he has the right to do so.

"Maybe many think that I have had the support and protection from Australia in the past 12 years, but the truth is that all who have helped me were Bulgarians. I have big trust in the Bulgarian people," he said.

His release followed an unprecedented statement by the head of Bulgaria's highest court urging the interior ministry to free Palfreeman immediately, saying his right to free movement was being breached.

Australian Associated Press