Joan Felt, his daughter, said he "slipped away" in his sleep after eating a large breakfast, the Post reported.
'Pride over role'
Felt's information was given to Woodward and Bernstein in a series of late-night meetings, which were immortalised in the book and film All the President's Men.
From the information that Felt supplied, the pair wrote a series of stories about the Nixon administration's role in the 1972 burglary of the Democratic National Committee headquarters at the Watergate complex in Washington.
Nixon resigned in 1974 following the scandal, becoming the first US president to do so.
Felt was "proud of everything Deep Throat did” and that he liked "being related to him", he told the CNN interviewer Larry King in a 2006 interview.
"He has always said that Deep Throat is a personality that was created by Bob Woodward, a name that was created. He likes to say that he is the person that they called Deep Throat," Felt’s daughter told King at the time.
When Felt admitted to magazine Vanity Fair in 2005 that he was the shadowy informant, he was both congratulated as a hero and derided as a traitor.
Nick Jones, Felt's grandson, called his grandfather "a great American hero" but former Nixon aides condemned what he did.
G. Gordon Liddy, a Nixon operative who served four-and-a-half years in jail for plotting the Watergate burglary, said that Felt "violated the ethics of the law enforcement profession".
In an interview subsequent to his unmasking as Deep Throat, Felt played down his part in the reporting of the Watergate scandal.
"I want to be remembered as a government employee who did his best to help everybody. I would like a reputation of trying to help people," he said.