Michael Palin and Terry Jones unveiled the plaque to honour the late actor, who died in 1989.
The pair were joined by Chapman's former colleagues Barry Cryer and Carol Cleveland at the unveiling at the Angel Inn pub in Highgate.
The plaque was organised by Chapman's friends and family members after English Heritage axed plans for an official memorial because of their budget cuts.
Referring to Jones's classic line from Life of Brian, the plaque describes Chapman as a "very naughty boy" and that he "drank here often and copiously".
Palin said: "This was Graham's manor and Graham was a lovely guy. I spent many happy times with him, most of which I forget.
"Highgate was his patch and he should be celebrated because he was a very good, brilliant, funny, nice, wise, kind man, who occasionally drank too much."
Barry Cryer added: "We did an awful lot of writing together, but also an awful lot of drinking together."
Graham Chapman's life will feature in the upcoming film A Liar's Autobiography - The Untrue Story Of Monty Python's Graham Chapman. The animation will feature his own audio recordings of the book.
Watch a trailer for the film below: