The guilty plea in youth court came as his trial was about to get underway Monday morning, in a high-profile case that's subject to a sweeping publication ban.
The accused was under 18 at time of the offence.
The judge has also placed a ban on the name of the teenage victim, who died a few days after the suicide attempt.
The Crown has withdrawn a second charge against the 20-year-old. His sentencing is set for Nov. 13 at 11 a.m.