O'Brien recounted his troubled childhood and said that while he did well in school and appeared to be a leader, he was using drugs and failed to seek help.
"I thought leadership involved saying the right things," O'Brien told the students. "But I never dealt with the things inside of me."
After spending more than two years in prison, O'Brien has written a book, started a roofing company in Great Falls and started a family with his wife, Gracie.
Great Falls High student council adviser Christine Baroch said O'Brien has a way of connecting with students.
"He's not presumptuous," she said. "He's a very humble and grateful man."
Shannon Ryffel, a senior from Highwood, said she believes the story of a fallen star trying to rise again is important for students to hear.
"I think it's really motivational and you can learn from other people's mistakes," she said.
O'Brien's speech was filmed by crews from ESPN's "Outside the Lines" series, as was a February board meeting in which O'Brien was hired to coach the Simms High School football team. The story is scheduled to air in June.
"I am just trying to be a football coach. I didn't ask for this," O'Brien said of the ESPN crew. "If this story can help somebody, that's what I'm all about."