Simon Gittany has been found guilty of murdering his fiancee, Lisa Cecilia Harnum, by throwing her off a high-rise Sydney apartment balcony.

Gittany, 40, stood stock still and his girlfriend Rachelle Louise started screaming as Justice Lucy McCallum handed down her verdict in the Supreme Court in Sydney on Wednesday.

Ms Louise yelled abuse at the judge, and was taken from the court in floods of tears.

Other family members stormed out of court and the judge briefly adjourned the verdict to restore calm.

Justice McCallum found Gittany was in a state of "uncontrollable rage" on the morning of Ms Harnum's death after he discovered she was leaving him.

"He maintained that rage and in that state, carried her to the balcony and unloaded her over the edge," Justice McCallum said.

In a verdict that took more than four hours to deliver, Justice McCallum gave a damning assessment of Gittany's character, finding he was "controlling, dominating and, at times, abusive" of Ms Harnum.

She found he lied "with telling ease" and distorted the truth when he took the stand in an attempt to discredit the woman he murdered.

"At many times in his evidence the accused struck me as being a person playing a role, telling a story which fit with the objective evidence but which did no more than that," Justice McCallum said.

"His account of what happened appeared to exist on borrowed detail.

"It lacked originality and the subtlety of actual experience."

Ms Harnum's family members smiled and embraced after the verdict was handed down.

In a judge-alone trial that gripped the public, the Crown alleged Gittany threw Ms Harnum off their 15th floor CBD apartment balcony on July 30, 2011 in a fit of "apoplectic" rage that she was planning to leave him.

Gittany maintained his innocence, saying Ms Harnum ran onto the balcony and disappeared over the edge as he desperately tried to reach her.

The trial heard allegations Gittany was brutal and controlling of his 30-year-old Canadian fiancee, subjecting her to the "most intense surveillance" imaginable.

Gittany installed CCTV in his apartment and used a computer program to monitor Ms Harnum's text messages, emails and internet usage.

He said he did so because she had a secret she refused to tell him.

Text messages showed Gittany was so jealous of other men, Ms Harnum had to look at the ground when she was outside, the court heard.

In the witness stand, Gittany admitted some of his behaviour towards Ms Harnum was controlling, but he emphatically and repeatedly denied he threw her off the balcony.

Sixty-nine seconds before her death, Gittany was captured on camera dragging Ms Harnum back into the apartment as she screamed "Help me, God help me".

But the defence claimed Ms Harnum, who suffered from bulimia, may have climbed over the balcony to escape Gittany, as a cry for attention or in a suicide bid.

Justice McCallum firmly rejected suggestions Ms Harnum was suicidal that morning or that she deliberately climbed over the balcony to escape Gittany.

"I have stood on that balcony," the judge said.

"I simply can't accept any person with a will to survive could have regarded it as an option for escape.

"Lisa Harnum may have been impulsive, maladaptive and over-sensitive. She may have been in a state of acute fear.

"... But I do not think she was deranged."

A tear-stained Ms Louise briefly emerged from court and asked the dozens of reporters surrounding her for a cigarette.

She refused to comment.

Waiting for Justice McCallum to return to the bench, Gittany's sister told him, "You didn't get a fair trial".

"I know," he replied.

An ambulance has arrived at the Supreme Court, believed to be for Gittany's mother, who was said by relatives to be "in a state" after the guilty verdict.

She was unable to return to court to say goodbye to her son as he was led away.

Gittany will face a sentence hearing in February.

Speaking outside court, an emotional Joan Harnum told reporters, "there are no winners in this case".

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

"We will always mourn the loss of our beautiful Lisa Cecilia and are working towards making her legacy a powerful wake-up call to young women.

"My daughter used to say people can ask for help but children and animals cannot.

"And now young women who are caught up in situations like my daughter found herself in need a voice as well."

Ms Harnum said her daughter's favourite saying was "families are forever".

"Please go home and hug your kids and hug your wife and husband and make it families forever for everyone," she said.