He said the experience of living with the ever-present threat of death had left him "mentally fatigued".

Mr Forbes will fly out of Sudan today a free man, after his murder conviction was annulled by the country's court of appeal.

Mr Forbes, 46, a construction engineer with Kenyan firm Trax International, was last month convicted of the murder of Ukrainian flight engineer Mykola Serebrenikov, who was found hanging from a towel rack in the company compound in the southern Sudan city of Rumbek in March.

Mr Forbes and three colleagues were convicted of murder, which is punishable by death in Sudan, despite an autopsy concluding the Ukrainian killed himself.

A panel of three judges, including the president of the court of appeal, yesterday annulled the convictions of the men, noting the lack of forensic evidence and the lack of evidence of a motive.

Because there was no dissenting decision, the ruling cannot be appealed. Mr Forbes last night said he was elated that his "bloody nightmare" had come to an end.

"Finally, after three months, justice and common sense prevailed," he wrote in an email to family and supporters.

"The relief we feel is beyond explanation."

'It was surreal'

In a separate email, Mr Forbes said: "After all the nonsense, illogical carry on, and lies we have been told by the police and the courts, it was surreal to be told in a matter of fact way that we had been acquitted.

"It is still sinking in slowly, maybe because I am so mentally fatigued by this experience.

"We haven't started to celebrate yet as I have been on the Sat Phone speaking to family and friends. I reckon tonight will be huge, although with my kidney condition I might have to hold back a bit."

Mr Forbes, who was born in Kenya but migrated to Australia 20 years ago and lived in Sydney and Brisbane before travelling back to Africa, is due to fly from Rumbek to the Kenyan capital, Nairobi, this afternoon.

A keen follower of rugby and cricket, Mr Forbes said he was looking forward to attending a rugby sevens tournament in Nairobi on the weekend.

He joked that one of the hardest things about his time in Rumbek's squalid prison was missing the cricket World Cup.

"The prison wardens had no idea what bribe I could have paid just to see the final on telly!"

Mr Forbes faced a possible death sentence after he and his colleagues were convicted over the death of a man found hanged in their compound, despite an autopsy finding that the man killed himself.

A Sudanese court annulled the murder verdict brought against Mr Forbes, three months after he was jailed.

James Phelps of Launceston in northern Tasmania says his friend needs medical treatment.

"They put him back into jail after the first court hearing and the malaria and kidney disease has been disastrous since then," he said.

"He flies into Nairobi at 5:30pm their time, and I imagine he'd pretty much go straight to the UN hospital."

TONY EASTLEY: For the past three months Australian George Forbes has languished in a filthy jail in Sudan, not knowing if he would face a death sentence or not.

Mr Forbes and three colleagues were convicted of murdering a man who was found hanged in their company compound in southern Sudan, even though a post mortem later found the man had committed suicide.

A court now has finally acquitted the men.

George Forbes has been telling Africa Correspondent Andrew Geoghegan of his relief to be free.

GEORGE FORBES: Finally common sense has come through. We always knew that our innocence would prevail; I suppose that's fantastic. I can't at this moment, really describe completely because it's not 100 per cent sunk in.

But all I can say is relief, a huge amount of relief.

ANDREW GEOGHEGAN: Can you understand how you came to be held in jail for three months and indeed how you were eventually convicted of murder?

GEORGE FORBES: It started off with the Minister of Law Enforcement stating in the papers that we murderers. And to back his political credibility, he then, what we believe, was compromised the police as well as the magistrate and then the high court judge.

ANDREW GEOGHEGAN: You were convicted, despite an autopsy finding that the man had hanged himself.

GEORGE FORBES: Correct.

ANDREW GEOGHEGAN: George Forbes, just take us back three months and describe what happened when you walked into the Trax compound and found this man.

GEORGE FORBES: We came back from dinner around about midnight and my security told me there was a kawager (phonetic), which is tinker for a white man, which had broken into the compound and he seemed to be very afraid of his life.

He was running from something, but what we didn't know. We felt that it would be better if he stayed in the room. We locked him there, not maliciously obviously, but we're in a post war town.

If he decided to run for it, he would probably have been shot and it was during that time that he decided to commit suicide. It was the next day that we were called to make our statement, and it was then that we got arrested.

ANDREW GEOGHEGAN: And you spent much of your three months in custody, in jail. Just describe those conditions.

GEORGE FORBES: Conditions that, well, not even fit for an animal. It's absolutely appalling. We weren't in a closed cell, we were in an open cell, so we were exposed to all the elements.

We were living pretty much in human faeces a lot of the time, there was a lot of cholera, typhoid, which I eventually contracted. A lot of very sick people in there.

ANDREW GEOGHEGAN: George Forbes, the maximum penalty for murder in south Sudan is death. Did you feel as though you could well have been sentenced to death?

GEORGE FORBES: They told us time and time again that we would be eventually sentenced and hung because you… under their law, you're sentenced to death in the manner the deceased was killed.

You know, it was too surreal for it really to sink in that we were really going to go that way, you know, all of us were too confident that one day, common sense would prevail and justice would be served.

TONY EASTLEY: Freed Australian George Forbes, talking to correspondent Andrew Geoghegan.

Brisbane businessman George Forbes plans to swap a putrid jail cell and the constant threat of execution for the beach, after being cleared of a murder charge by a Sudanese court.

Mr Forbes was living among human faeces and tropical disease with a promised fate of death by hanging before being freed from a southern Sudan jail overnight.

The 46-year-old Australian and three other men - two Kenyans and a Sudanese - were charged with murder three months ago.

Mr Forbes and the other three were all employees of a Kenyan-based aid and development company working in Rumbek.

They were convicted of murder by a lower court following the death of a Ukrainian man in their compound and faced the death penalty, but an autopsy had reported the man's death was consistent with suicide.

A panel of three judges, including the president of the court of appeal, yesterday annulled the convictions of the men, noting the lack of forensic evidence and the lack of evidence of a motive for the killing.

Because there was no dissenting decision, the ruling cannot be appealed against.

Mr Forbes's brother-in-law Orson Taylor said the businessman was due to arrive in Nairobi, Kenya, about 1am (AEST) tomorrow.

"I'm not sure what his plans are," Mr Taylor said.

"But I would expect him to spend a couple of days here in Kenya before going back to Australia.

"Early on when this ordeal started he talked about going down to the coast for a week.''

Australia's parliamentary secretary for foreign affairs Greg Hunt said Mr Forbes's health, which had deteriorated while he was in jail in Rumbek, had made very significant progress.

"Finally commonsense has come through - we always knew that our innocence would prevail," Mr Forbes told the ABC's Africa correspondent.

His three months in the open cell left him exposed to nature's elements and infectious disease.

"Conditions [were] not even fit for an animal," he said.

"We were living pretty much in human faeces a lot of the time.

"There was a lot cholera, typhoid, which I eventually contracted."

The maximum penalty for murder in southern Sudan is death, which he was reminded of many times during his incarceration.

"They told us time and time again that we would be eventually sentenced and hung," he said.

"It's too surreal really to sink in that we were going to go that way."