The couple had been arguing for months, with Ms Howell giving Charlton four weeks to leave her home in Melbourne's southeast.

But instead of leaving, the prosecution said Charlton murdered Ms Howell on the evening of April 21, after another one of their arguments.

He pleaded not guilty and claimed he had returned home after walking his dog to find her bloodied and lifeless body at the bottom of the stairs inside the Hughesdale unit.

His defence lawyers tried to pin the murder on alternative suspects, including an ex-boyfriend or her estranged brother.

But after just over one day of deliberations, a 12-person jury returned to the court on Thursday afternoon and delivered their guilty verdict.

Charlton, who has been on bail throughout the trial, collapsed to the ground in the court dock moments after he heard the verdict, with custody officers and a woman rushing to his side.

He lay on the floor as the jurors were removed from the court, and a code black emergency and paramedics were called.

Charlton was later placed in a wheelchair and taken out of the court to a private room by two paramedics, with defibrillators attached to his chest.

He was rushed to St Vincent's Hospital about 5pm, where he will be assessed under the guard of custody officers.

Ms Howell's family, who have attended every day of the trial, cried upon hearing the jury's verdict.

"Twelve random people have validated what we've believed for 16 years so it's just a weight lifted off our shoulders," Ms Howell's nephew Nathan Harris said outside court.

Lisa Hennessy said she was "over the moon" that justice had finally been served for her beloved sister.

"We're just so happy that Jo got her result, it's all about her," she said, outside court.

"The tears just kept coming because I kept thinking of her."

Charlton will return to court later this year for a pre-sentence hearing.