Felt died of congestive heart failure, according to family friend John O'Connor.
Felt admitted in 2005 he was the Washington Post's source for many of its 400 stories on the Watergate affair during the early 1970s. The Watergate break-in eventually led to the 1974 resignation of President Richard Nixon.
"I'm proud of everything that Deep Throat did," Felt, 92, told CNN's "Larry King Live" in 2006, his first public interview on the subject.
Felt's entanglement with history occurred in 1972 after the bungled break-in at the Democratic National Party offices in the Watergate building. Felt said he was unhappy with the way the administration meddled with the FBI investigation into the break-in which led him to divulge information to the newspaper.