The TV spot began airing across the country on Monday.
"I feel like most people in their lifetime have been bullied at some point, and I think that it's about time that people start making a change," Bieber said, adding that incidents often get brushed under the rug by principals, teachers and other students.
"I think the movie is really powerful and it can help change a lot of lives," Bieber added.
Bieber also wants bystanders to speak up to stop bullies. In a news release, Bieber encouraged his fans to watch the movie with their friends and help start the conversation to end bullying.
"My fans are always up for supporting a great cause. It's one of the things I'm most proud of as an entertainer," Bieber said.
The pop star is one of many celebrities who have thrown their support behind the film, including Johnny Depp, Ellen DeGeneres, Meryl Streep, Kelly Ripa and Anderson Cooper.
The film "Bully" opens nationwide Friday after playing only in a few theaters since last month. The film is rated PG-13.