John McLellan, who is now communications director of the Scottish Conservatives, was at a Tory rally in the city where Mr Cameron was addressing around 150 members of the party.
The event at the city’s Great Central Hotel was interrupted by an protestor who started shouting “No cuts” as the Prime Minister was giving a speech.
But John, who has played rugby for the Watsonians team in Edinburgh, tackled the intruder before he was taken away by Special Branch.
The incident was initially reported by the Scottish Sun, which described John as a “burly spin doctor”.
Afterwards the former editor tweeted: “Years of missed tackles and I finally nailed one this afternoon at PM event. All in the line of duty, sir.”
John was axed by The Scotsman earlier this year in a restructure by Johnston Press.
But he bounced back in his new role for the Scottish Conservatives in June, which includes advising new leader Ruth Davidson on “communications strategy, direction and content”.