Judge Anne Derrick said the man was aware of what he was doing when he stabbed his 17-year-old girlfriend in December 2010.
Derrick said the evidence presented satisfied her beyond a reasonable doubt, saying that the teen was aware of what he was doing and intended to kill the victim.
Steve Drake, the prosectutor in the case says the Crown is satisfied with the verdict.
"Well the judge basically found that (he) had intentionally committed the murder, despite the fact that there was some level of intoxication," says Drake, "the requisites for second degree murder were all met and the Crown proved every element of the case beyond a reasonable doubt."
The girl had 104 wounds, from several different knives, one of which was broken off in her body.
The now 18-year-old man is waiting for his sentencing dates.
He was 16-years-old at the time of the incident.
A sentencing hearing is scheduled for Nov. 26. Drake says he will argue for an adult sentence of life in prison.
The identities of the convicted and the victim are protected by the Youth Criminal Justice Act.
Victim's family applauds verdict
When the judge read the verdict, the teen turned to face the crowd in the courtroom, and the victim's family applauded.
A relative of the family remarked they weren't afraid of him. That prompted the teen to make an obscene remark.
The judge then rose behind the bench and warned the gallery she would not tolerate such a reaction.
Teen 'doesn't remember' day girlfriend was killed
The 18-year-old testified that he doesn't recall any of the events from that day, starting from the afternoon, when he took some pills and drank moonshine.
He said he doesn't remember anything else until the police woke him up in a cell at about 4 a.m.
In court, he said he didn't believe his girlfriend was dead until he saw a picture of her body.
He said the two had been dating for four months at the time of his girlfriend's death. He told the court he loved her.
Defence called for manslaughter
The defence had asked the court to consider a manslaughter charge.
His lawyer, Darlene MacRury, argued her client was severely intoxicated by drugs and alcohol, and was caught up in the heat of passion, provoked by the knowledge that the victim had cheated on him three times.
The Crown said the defendant's actions showed deliberate intent and mental control, like when he broke a knife in the victim's body and went to find another one to continue stabbing her.
In the courtroom people wore t-shirts with the victim's picture and the line "Remember Me."