Steven Boone was also found guilty of two counts of administering a noxious substance —his semen — and one count of attempting to do so.
He was acquitted of two counts of aggravated sexual assault relating to oral sex with two men.
The verdict was reached Wednesday evening.
The first charges were laid against Boone in 2010 after a then-17-year-old Ottawa man came forward to police.
He had tested positive for HIV after having unprotected sex with Boone several times, and he said Boone never told him he had the disease.
Ottawa police then released Boone's photo in a media release asking any other potential victims to come forward.
Verdict comes month after Supreme Court ruling
Thursday's guilty verdict comes after a controversial Supreme Court of Canada ruling last month, which states people are not required to disclose if they have HIV unless their viral load count is deemed high enough to potentially infect someone with the disease.
The Supreme Court of Canada also decided condoms would have to be worn for the viral load consideration to be taken into account.
Carissima Mathen is a criminal and constitutional law professor at the University of Ottawa, who has done research about the criminal responsibility of failing to disclose HIV status.
"Attempted murder is really about the intent of the defendant, what was the defendant's state of mind," Mathen said Friday. "And as long as you can show an intent to kill, combined with some action that takes it beyond mere preparation or just thinking about it, that's enough to show attempted murder.
"The issue around failure to disclose HIV is that because that's an area where there can be different motivations at work, it can be a little bit tricky, or possibly a slippery slope to start to think that everyone who deliberately withholds that information — maybe because they're just careless or they're not thinking about the other person — will there be a temptation to say, well, they must have intended to kill the person," she said.
Many in the gay community believe criminalizing HIV non-disclosure will cause some people to avoid getting tested.
During the trial, the Crown relied heavily on sexually explicit online chat history, in which Boone would seek sex with HIV-negative men.
Boone is facing similar charges in Ottawa on Nov. 13, and still more similar charges in Waterloo next month.
He is expected to be sentenced after the second Ottawa trial ends.