Jessica Silva wins appeal over stabbing of violent partner James Polkinghorne

Jessica Silva dealt with her violent drug-addled boyfriend's abuse for so long, she thought she could change him.

But on Mother's Day 2012, James Polkinghorne told her over the phone: "I'm going to cave your f---ing head in" and "I'm gonna break your f---ing jaw 'cause you're a dog."

Hours after making the threatening phone calls, he turned up to her parents' home, in Marrickville, in Sydney's inner west, high on ice and in a violent rage.Ms Silva stabbed Mr Polkinghorne five times in the back and face outside the house.

In late 2014, a NSW Supreme Court jury found Ms Silva not guilty of murdering Mr Polkinghorne , convicting her of the lesser charge of manslaughter.

The trial judge found that she killed Mr Polkinghorne "under extreme circumstances in the agony of the moment", and spared her jail time.

Ms Silva appealed against the conviction, arguing she was acting in self-defence.

On Wednesday, the NSW Court of Criminal Appeal quashed her conviction, in a majority decision of three judges.

Ms Silva threw back her head in relief, and was embraced by family members.

Jessica Silva leaving the NSW Supreme Court in June. Photo: Ben Rushton

There were loud whispers of "wow" in the public gallery as Justice Lucy McCallum briefly announced the decision.

Earlier this year, Ms Silva's barrister Gregory Scragg told the appeal court: "She was entitled to defend herself and what she did, in the circumstances, was entirely reasonable."

The court heard that Mr Polkinghorne was abusive from an early point in their four-year relationship, and the violence escalated during 2011 and 2012.

Ms Silva said: "I dealt with it for so long, I thought I could change him."

Mr Scragg said Silva also believed Mr Polkinghorne had previously shot and killed Nikolas Argiropoulos, whose body was found in a Birchgrove park.

When Mr Polkinghorne arrived at Ms Silva's family home, he struggled with her brother and father outside.

She went back into the house and grabbed a knife from the kitchen, and remembered stabbing him once, "maybe twice".

During the appeal, Crown prosecutor Neil Adams argued that Ms Silva's response to the threat of Mr Polkinghorne was not reasonable, noting the number of times she stabbed him and the fact that she did not call the police.

"The opportunity to call the police in circumstances where she was significantly under threat was not taken.

"One would have expected her to make some other attempt to call the police," Mr Adams said.