Stephen Roy Standage has been found guilty of the murders of Ronald Jarvis in 1992 and John Thorn in 2006 in Tasmania's longest running criminal trial.
It took the jury more than 16 hours to reach its verdicts, after a trial that lasted more than five months.
As the verdict was being read out, Justice Stephen Estcourt had to tell the family and girlfriend of Ronald Jarvis to be silent after they began cheering in court.
Adam Thorn began crying when the jury found Standage guilty of his father's murder.
Standage did not react.
Outside the court the families hugged former cold case detectives who handled the investigation that lead to Standage's 2010 arrest.
Victim impact statements will be presented when the court resumes this afternoon.
Earlier in the trial the court heard 61-year-old Standage supplied Mr Jarvis with cannabis and owed him between $6,000 and $20,000 at the time of his disappearance.
Standage has spent the past 22 years denying any involvement in Mr Jarvis' death.
He also pleaded not guilty to murdering John Thorn, arguing Mr Thorn was his best mate.
Standage's lawyer had argued there were significant differences between the killings, making it unlikely the victims were shot by the same person.
The prosecution focused on the similarities of the murders: that Standage was the last to see both victims and that both had been taken to bush locations, shot in the head and covered with saplings.
Money and drugs were offered as motives for both killings.