Hunter Moore, 28, faces between two and seven years in prison, according to the US Attorney's Office.
He ran IsAnyoneUp.com, on which pictures were posted of naked women without their consent, and was once called "the most hated man on the internet".
Another man allegedly involved has pleaded not guilty and faces trial.
As well as running the site - where people often posted pictures of their ex-lovers, coining the term "revenge porn" - prosecutors said Moore had also enlisted a hacker to steal nude photos from email accounts.
Photos posted between 2010 and 2012 included pictures of an American Idol finalist, the daughter of a major US Republican party donor and a woman in a wheelchair, according to a 2012 article in Rolling Stone magazine.
Moore alleged in the agreement that he had paid Charles Evens to hack email accounts and steal photos.
Mr Evens, 26, of Los Angeles, pleaded not guilty and is scheduled for trial in March. He refused to comment.
Moore is due in court on Wednesday 25 February, although the Attorney's Office spokesman said sentencing could be postponed until March. Moore will also be required to inform his parole officer every time he uses a new device capable of accessing the internet.
Moore was arrested in January 2014 after an FBI investigation. He had previously been ordered to pay $250,000 (£170,000) in damages for defamation after a civil lawsuit.
He was found to have made false claims on Twitter that James McGibney, the chief executive of an anti-bullying website, was a paedophile who possessed child pornography.