Mark Forstater brought a High Court lawsuit against the anarchic comedians over the show, which is based on the 1975 movie "Monty Python and the Holy Grail."
Forstater produced the film, and his lawyers claimed it was agreed that he would be "treated as the seventh Python" financially, entitled to the same share of "Holy Grail" merchandising and spin-off income as the other members.
That amounts to one-seventh of the first 50 percent of income from "Spamalot," but lawyers for the Python troupe said he was entitled only to one fourteenth.
A global hit, "Spamalot" ran on Broadway for almost four years to 2009 and is still playing in London's West End.
At a hearing late last year, member Michael Palin said that the idea of a seventh member "was never going to be accepted by the Pythons."
And he disputed Forstater's claim to have helped written the film, saying: "There were six of us. We were a tight group. We wrote our own material."
Judge Alastair Norris ruled in favor of Forstater in his suit against the five surviving Pythons: Palin, Eric Idle, Terry Jones, John Cleese and Terry Gilliam. The sixth member of the troupe, Graham Chapman, died in 1989.
Forstater, 69, said he was happy with the judgment, and estimated he was entitled to more than 200,000 pounds ($300,000).
"Justice has prevailed," he said. "There is a sadness, though, about having to face people who were my friends in court.
"The friendship has gone. Terry Gilliam and I used to share a flat. We go back 51 years."
And, he added, "I still think they are very funny."
Members of the Python troupe were not in court for Friday's judgment. There was no word on whether they would appeal.