Two brothers, accused of lighting fires inspired by Islamic State ideology, have been acquitted of terrorism charges in a landmark trial.

Ari Sherani, 22, and Aran Sherani, 21, both from Epping, were found not guilty of attempting to commit a terrorist act after they set bushland near Humevale ablaze with petrol in the summer of 2021, mirroring the devastating Black Saturday fires.

However, Aran was found guilty of acts in preparation for terrorism due to his association with the Islamic State, purchasing a knife, and recording threatening videos.

During the three-week Supreme Court trial, jurors saw videos of Aran pledging allegiance to the Islamic State, vowing revenge against non-believers, and setting trees alight.

Aran's defence claimed he created these videos to convince the Islamic State to support his travel to the Middle East to aid the Kurdish people.

After five days of deliberations, the jury returned the verdict, prompting emotional embraces between the brothers. Ari was released, while Aran remains in custody.

Justice Amanda Fox commended the diligent jury before Ari's release. Aran's sentencing will occur at a later date.