A one-time volunteer firefighter was convicted Tuesday of starting a huge blaze that killed 10 people during Australia's horror 2009 "Black Saturday" inferno.

Brendan Sokaluk, 42, was found guilty of 10 counts of arson causing death by a Victoria Supreme Court jury over a 36,000-hectare bushfire in the town of Churchill on February 7, 2009, which razed 156 homes and killed 10 people.

He faces a maximum 25-year jail term on each of the counts, and his conviction makes him Victoria state's worst killer.

Sokaluk, once a volunteer with the Country Fire Authority, admitted starting the fire but told police he had dropped cigarette ash out of his window and it had been an accident.

The month-long trial heard that Sokaluk, who has autism and a mild intellectual disability, had been seen in the area by witnesses but gave conflicting stories about his movements that day.

He was charged soon after the so-called "Black Saturday" disaster, a series of simultaneous fires which raged in extremely high, dry and windy conditions, destroying more than 2,000 homes and killing 173 people.

It was Australia's deadliest natural disaster of modern times.

Sokaluk has only been linked to the Churchill blaze but became the focus of intense public emotion over the firestorm and had to be held in isolation after threats were made against him and his family.

He was remanded in custody and will be sentenced at a later date.