The 18-year-old "Mercy" crooner and 26-year-old "Starboy" singer attended the annual awards show at Ahoy Rotterdam arena in Rotterdam, Netherlands.
Mendes was nominated for four awards, including Best Pop and Biggest Fans, and walked away with Best Male and Best Canadian Act. He performed a rousing rendition of "Mercy," his newest single, at the ceremony.
The Weeknd was also up for Best Male and Best Canadian Act, and won Best Video for "Starboy" featuring Daft Punk. He performed the song in a glittering stardome at the awards show.
Lady Gaga and Justin Bieber weren't present at the event, but took home two and three awards, respectively. Lady Gaga won Best Female and Best Look, while Bieber tied for Best Canadian Act and took Biggest Fans and Best Song for "Sorry."
The Get Down actor Jaden Smith, The Vampire Diaries alum Nina Dobrev and Bollywood star Deepika Padukone were among the presenters. Smith handed off Best New Act to Zara Larsson, while Dobrev and Padukone presented The Weeknd with Best Video.
"Mercy" appears on Mendes' latest album, Illuminate, which also includes the single "Treat You Better." "Starboy" will appear on The Weeknd's forthcoming album of the same name, which is scheduled for release Nov. 25.