Dirani and another man were accused of supplying a 1942 Smith & Wesson revolver to the teenager at Parramatta Mosque. 

After obtaining the gun, the boy walked to police headquarters dressed in traditional Islamic clothing, shot Mr Cheng and was then killed in an ensuing gunfight.

Dirani, 22 at the time of the murder, always denied he had any connection to the plot and pleaded not guilty. 

"After the shooting of Mr Cheng was reported, Mr Dirani put posts on social media which suggested he did not know of the plan," Justice Deborah Sweeney said in the NSW Supreme Court on Friday.

While no footage showed the actual gun changing hands, the jury found Dirani guilty of involvement in the terrorist plot on the Crown's circumstantial case against him.

Dirani was "involved only for a short time and in a limited way" in the conspiracy to murder Mr Cheng, Justice Sweeney said, and noted the prosecution's case had narrowed. 

The verdict brought an end to a complicated judicial process that stretched over eight years. 

“It would be fair to say the criminal justice system has not worked well in Mr Dirani's case," Justice Sweeney said of the delay, which was taken into account in reducing his sentence. 

The maximum penalty for the offence is life imprisonment.

Dirani appeared via video link from prison, where he has been on remand since 2015, with a shaved head and long beard, holding his head in his hands throughout much of the sentence. 

He will be eligible for parole if approved by the attorney-general in May 2026, with his full jail term expiring in November 2030.