Smith was a talented junior swimmer and won a string of Australian Junior Championships, but in his late teens ice pushed his life off the rails and he was soon living on the street.
"It was difficult, but I guess the pain that I suffered, the pain that I dealt with has actually put me in a position now to give back to others," he said.
"That's what my life's all about now. I'm all about giving hope to the next generation and giving hope to other people who are addicted to drugs."
Smith said his five-year drug and alcohol addiction not only affected his swimming career, but his family relationships as well.
"I destroyed my family and they're still healing now from the whole situation," he said.
"You can understand what it'd be like watching your son literally destroy his life."
His mother Julie Smith said it was a difficult period for their family.
"We felt for him because we knew it wasn't him," she said.
"We just didn't know what to do.
"We saw psychologists and psychiatrists, everything, and nobody could give us an answer on how to help him."
Smith said it was his love of the pool and his faith that helped him get his life back on track.
Earlier this year he finished fourth in the 200 metres freestyle at the Australian Swimming Championships in Adelaide to secure his spot in the relay team in Rio.
Smith's long-term coach Dennis Cottrell said it was an incredible achievement.