The 50-year actor told NBC "Today" show host Matt Lauer that he was diagnosed about four years ago but he's not sure how he contracted the virus that can cause AIDS.
"I'm here to admit that I'm in fact HIV-positive," Sheen said.
"It started with what I thought was a series of crushing headaches," he explained. "I thought I had a brain tumor. I thought it was over," he said, adding, "It's a hard three letters to absorb. It's a turning point in one's life."
Sheen said he made the announcement to put an end to extortion efforts. He revealed that he had paid millions to buy people's silence on the private matter.
"I have to put a stop to this onslaught, this barrage of attacks and of sub-truths and very harmful and mercurial stories that are about me, that threaten the health of so many others that couldn't be further from the truth," he told Lauer.
When asked what untrue report hurt him the most, Sheen said it was upsetting to hear people claiming that he knew he had the virus and "was intentionally spreading it," which is not the case, he noted.
Sheen said he has told all of his sexual partners about his diagnosis.
At one point Lauer read Sheen supportive messages from fans weighing in on social media. Sheen's response? "I'm going to ride this wave of support."
Going forward Sheen said he would do what he can to raise awareness and help others.
"I have a responsibility now to better myself and to help a lot of other people and hopefully with what we're doing today others will come forward and say, thanks Charlie," he said.
During his TV appearance Sheen said he's no longer doing drugs, but still drinks "a little bit."
Prior to his "Today" appearance the National Enquirer said it had done "an exhaustive 18-month investigation" into the life of Sheen, revealing the news this week.
Sheen has had a history of substance abuse and famously made headlines in 2011 amid what appeared to be a public meltdown, during which he popularized his catchphrase "Winning!" Around that time, he parted ways with his long-running role on CBS' "Two and a Half Men."
Sheen was married to Brooke Mueller from 2008-2011, Denise Richards from 2002-2006 and Donna Peele from 1995-1996. The former "Two and a Half Men" star has had a long dating history, having been linked to porn stars and models, along with such high-profile actresses as Winona Ryder, Robin Wright and Kelly Preston.
In October 2014, Sheen and his fiancee, adult film star Brett Rossi, ended their eight-month engagement.
"She's a terrific gal -- but we've mutually decided to go our separate ways and not spend the rest of our lives together," he said in a statement.
The New York City-born actor has largely kept a lower-profile this year. The actor, who starred on TV in "Anger Management" and "Two and a Half Men," made an appearance earlier this year on "The Goldbergs," reprising his role from "Ferris Bueller's Day Off." In 2010, he was named the highest-paid actor on television.
Sheen's film roles include "Platoon," "Wall Street," "Eight Men Out," "Major League" "Being John Malkovich," among many others. More recently he appeared in "Scary Movie 5," "Wall Street: Money Never Sleeps" and "Due Date."
Looking ahead, Sheen says he plans to keep working and has some movie and TV roles lined up.