Henry Keogh has had his conviction for murdering his fiancee in 1994 overturned and a retrial ordered by the Court of Criminal Appeal.

Mr Keogh had been serving a life sentence, with a non-parole term of 25 years, for allegedly drowning Anna-Jane Cheney in a bath at their Adelaide home.

Today the appeal court set aside Mr Keogh's conviction and ordered a retrial after ruling there was new information to suggest forensic pathology evidence presented at his trial almost 20 years ago was flawed.

Mr Keogh brought his appeal after new legislation, passed last year, allowed for a case to be reheard on the basis of fresh and compelling evidence.

He will apply for bail on Monday, an application that was not opposed by the prosecution.

University of Dundee forensic pathologist Professor Derrick Pounder had told the court that the 1994 autopsy of Ms Cheney was inadequate.

Professor Pounder said the failure to weigh the heart of the alleged victim was just one of several failings.

He said the detail and description provided in the report, by then chief forensic pathologist Colin Manock, was far below the standard expected at that time.

He also said standards were even below those Dr Manock had taught him when they worked together at Adelaide's Forensic Science Centre.

A step in the right direction but disappointing: Supporter

Supporter Gordon Wood described the court ruling as "politically safe". ( ABC News )

Outside court, supporter Gordon Wood, who served three years' jail before being acquitted on appeal of the 1995 murder of model Caroline Byrne, described the ruling as "politically safe".

Mr Wood said while it was a step in the right direction, he was disappointed.

"We hoped for an acquittal because there isn't sufficient evidence to support a theory of murder, let alone an act of murder," he said.

"It's a very difficult thing for the court to probably deliver that in one fell swoop."

Bob Moles, a legal reform activist and Keogh supporter, said setting aside the conviction was a good start.

"We first said the conviction should be set aside 15 years ago and it's taken us all this time to actually get the correct decision from the court," Dr Moles said.

"This is a turning of the tide for South Australia and nationally as well."

Dr Moles said the court had no choice but to set aside the conviction after the prosecution's own independent experts said the forensic evidence did not support any theory of murder or criminal assault.

"When you have your own experts telling you, you don't actually have a forensic case to back this up, then you don't really have anywhere else to go with this."