Simon Gittany will be sentenced today for murdering his fiancée by throwing her off the balcony of their Sydney apartment.

Senior Crown prosecutor Mark Tedeschi has called for a sentence of at least 20 years for Gittany, who was found guilty of murdering Lisa Harnum in 2011.

The Supreme Court has heard he threw her from the balcony of their 15th-floor inner city unit because she planned to leave him.

The court has heard Gittany is a cold and calculated killer who has shown no remorse.

But his barrister has called for a lighter sentence than the minimum 20 years in jail, arguing he is unlikely to reoffend.

During his sentencing hearing last week, the Crown introduced a surprise new witness who was Ms Harnum's friend.

The witness said Gittany "frequently threatened Lisa Harnum with death if she ever left him".

The defence has called for the new evidence not to be considered in sentencing as "it's way too late".

Gittany will be sentenced this morning in the Supreme Court by Justice Lucy McCallum, who presided over his judge-only trial.

During the trial the Supreme Court heard that Ms Harnum told a personal trainer and a counsellor that restrictions had been placed on her clothing, hair, work and general movements.

There were CCTV cameras both inside and outside the couple's unit and Gittany was secretly monitoring Ms Harnum's text messages through a computer program he installed on her phone.

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.

He was accused of being "apoplectic with rage" when he discovered Ms Harnum's plans to leave him and return to Canada.

Just 69 seconds before Ms Harnum's death, Gittany was captured on CCTV, physically restraining her and dragging her back inside the unit she had tried to flee.

In handing down her verdict in November, Justice McCallum said the circumstances of Ms Harnum's death were shocking and tragic.

She said there was no doubt Gittany was "controlling, dominating and at times abusive".

Gittany, 40, maintains he did not kill Ms Harnum and insists she climbed over the glass balustrade herself and fell.

But Justice McCallum did not accept Gittany's account.

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".