Simon Gittany has been found guilty of murdering his fiancée Lisa Harnum by throwing her off the balcony of their Sydney CBD apartment.

Justice Lucy McCallum delivered the verdict to a packed Supreme Court after a mammoth judgement that stretched for four-and-a-half hours.

She characterised Gittany as a jealous and controlling man who had flown into a rage when he found out his fiancée was leaving him.

She told the court she did not accept Gittany's account that Ms Harnum climbed over the balcony of their 15th floor apartment before falling to her death in July 2011.

The judge said the lack of fingerprints on the glass barrier made his version of events implausible.

Justice McCallum also dismissed suggestions Ms Harnum had suicidal tendencies or would have self-harmed, telling the court they were "completely unfounded".

Girlfriend's outburst after guilty verdict announced

Dressed in a suit, the 40-year-old Gittany barely reacted as he was found guilty.

However, the judgement prompted an outburst from his current girlfriend Rachelle Louise, who screamed at the judge "you're wrong".

The outburst continued as she was was removed from the court in a flood of tears.

Other family members stormed from the court after the judgement, while an ambulance was called for Gittany's mother who family members said was left "in a state".

Gittany's girlfriend walked out of court. Can still be heard screaming outside. Very little reaction from Gittany himself. — Lucy Carter (@lucethoughts) November 27, 2013

The public gallery was packed for the climax of the judge-only trial, which Justice McCallum told the court had attracted an "unprecedented level of public attention".

Simon Gittany's girlfriend, Rachelle Louise. ( AAP: Dan Himbrechts )

The judge said at the time Ms Harnum fell 15 floors from the couple's balcony, Gittany was a jealous lover who monitored his fiancée's text messages.

Justice McCallum told the court Gittany was controlling and at times abusive towards his partner. She said his behaviour represented an "inexcusable breach of trust", but said she was confident the couple loved each other.

The judge was also critical of the evidence given by Gittany during the trial, including his account of how Ms Harnum died.

"I found it unconvincing," Justice McCallum said.

"A person playing a role, telling a story that fitted the objective evidence, but no more than that."

Key witness crucial in guilty verdict

The judge told the court the evidence of one witness in particular was crucial to the prosecution's case.

Josh Rathmell was walking through Hyde Park, across the road from The Hyde, on his way to work at the time of Ms Harnum's death.

Mr Rathmell told the trial the sound of male screams drew his attention to the 15th floor balcony, where he saw a man with no shirt on unloading an object or items he initially thought were luggage or rubbish.

While the judge did not definitively say whether she accepted Mr Rathmell's evidence, she described it as "a careful and compelling account".

She said there was nothing implausible in the suggestion that Ms Harnum was rendered unconscious before being thrown from the balcony.

Key evidence from Gittany trial The tragic final moments of Lisa Harnum's life were replayed in a murder trial that has captured the public's attention. Look back at the key evidence.

"It is worthwhile to note the speed and strength used by the accused to stop Ms Harnum as she ran for the lift," Justice McCallum said, referring to CCTV footage captured just over a minute before Ms Harnum fell to her death.

The court was told Gittany "berated" his fiancée for looking beautiful and did not want her to associate with her workmates.

Justice McCallum said by the time of her death, Ms Harnum felt sad and alone.

Ms Harnum's mother, Joan, addressed the media after the verdict, saying "there are no winners in this case".

She says she wants the story of her daughter's death to used to raise awareness about the dangers of controlling relationships.

"Two families have had their lives dramatically changed forever," she said.

"We will always mourn the loss of our beautiful Lisa Cecelia and are working towards making her legacy a powerful wake up call to young women, parents and sibling of these young women to be aware of the warning signs of a controlling relationship."

Gittany's sentencing hearing is scheduled for February.