Christopher Cullen sat back in the dock with a self-satisfied smile when his wife's former lover walked into the courtroom.

Nick Baastrup, a tall young Danish man, sat metres away from Cullen, and detailed his two-month affair with Victoria Comrie Cullen in late 2013.

It was Cullen's case that Ms Cullen had taunted him about her sex life on January 22, 2014, and he slit her throat in a deserted fishing club car park in Taren Point, in an act of provocation and self-defence.

The 51-year-old Englishman appeared to revel in the evidence of Mr Baastrup, a key witness, who confirmed Cullen's long-held and obsessive suspicion that his wife had a boyfriend.

But what was likely to be more important to the jury of eight men and four women was the overwhelming evidence that Cullen had long been abusive, domineering, and manipulative.

Cullen had pleaded guilty to manslaughter on the basis of provocation and self-defence, but on Tuesday the jury found him guilty of murder.

Outside court, Ms Cullen's friend Renee Jomaa said her death was devastating, and would have a lasting impact. "The trial detailed Comrie's brave battle as a victim of domestic violence, and a terror she did not escape," Ms Jomaa said, through tears.

The three-week trial in the NSW Supreme Court was told that  Ms Cullen, a 39-year-old Irish beauty therapist, was usually bubbly, vivacious, and loved by her clients at Lush Hair and Body in Sylvania Waters.

But in the year before her death, she told friends her marriage was "loveless", Cullen was violent and sometimes raped her.

She began talking to her parents in Northern Ireland on Skype while hidden in cupboards, telling them she was frightened of Cullen and wanted to leave.

Cullen came to believe that his wife was having an affair and began calling her a "slut" and a "whore" in public.

He tried to control her social and working life, demanding Ms Cullen cut down her hours at the salon.

The breaking point was in October 2013, when Ms Cullen came home late from a night out and her husband pushed her up against a wall, held her by the throat, and kicked her out of their Sylvania house.

From there, things escalated as Cullen began harassing his wife at her work, by dumping her clothes on the footpath, and holding up signs scrawled with "Comrie Cullen is sleeping with clients".

Police successfully applied for an apprehended violence order on her behalf, as the couple faced several court cases.

On the morning of her death, a local court ruled in her favour in a civil case about the couple's car, and Cullen came to her flat.

Neighbours heard the high-pitched screams of a woman coming from the garage, and the jury was told it was likely that Cullen punched her in the face and bundled her into the boot.

He then bought two long-bladed fishing knives, labelled "guaranteed sharp", and a change of clothes and drove to the fishing club at Woolooware Bay.

Hours after a passerby found her body and called police, Cullen emerged from the mangroves with self-inflicted wounds on his torso, saying he'd "lost it", but the couple had stabbed each other.

Cullen tenaciously held on to the argument that he had acted in self-defence and had been provoked by his wife, often scrawling notes in court, looking angrily at witnesses who gave evidence against him, and talking about documents with his lawyers in his thick Liverpool accent.

But at 2.05pm, he was taken down into the cells, a convicted wife murderer.

The sentencing process will begin next week.