O'Brien worked on the newsmagazine programs "The Insider" and "Access Hollywood," but made headlines in 2005 when he left slurred voicemail messages asking a woman to join him for drugs and sex.
After a stint in rehab to be treated for his long-term battle with alcoholism, he returned to "The Insider," but was fired from the show in 2008 after he sent an offensive e-mail about his co-host Lara Spencer to colleagues, the Post said.
"I was not in total recovery at the time. I was still messed up," O'Brien told the newspaper.
He said he has been sober for more than 600 days and is considering job options.
His book, tentatively titled "I Love Your Work," is to be published by St. Martin's Press, the Post said.