Mark Moore's lawyer Peter Bawden confirms a jury found his client guilty of all four counts.
Various media reports say the four men were killed in three separate incidents between June and November of 2010 _ reportedly the same two guns were used in the shootings.
Moore was charged with the slayings of Jahmeel Spence, 27, Courthney Facey, 18, Mike James, 23, and Carl Cole, 45.
The lead Toronto police investigator told reporters on Saturday that the crimes were "completely senseless."
Hank Idsinga said the theory presented by the Crown during the trial was that Moore, who was trying to be a rapper, killed the men to build street credibility as a gangster.
The defence argued during the trial there was no direct evidence that Moore possessed the guns throughout the 75 day period the four men were killed and there was room for a reasonable doubt.
First-degree murder convictions carry an automatic life sentence with no chance of parole for 25 years _ media reports say a formal sentencing hearing is set for June 16.
Moore, 31, is reportedly already serving a 12 year sentence for armed robbery.