After consulting with the Twitter hive mind, it seems the most comparable precedent for what Brian Topp would be trying to do is Brian Mulroney. Mr. Mulroney worked within the Progressive Conservative party before becoming leader. He, though, only won the leadership on his second try and that, along with his public profile in general, makes the comparison to Mr. Topp imperfect.
A few other names to include in this discussion: Stephen Harper, John Tory, Ed Miliband and David Cameron.
Messrs Harper, Miliband and Cameron were party strategists, but each won election as an MP before seeking their respective party leaderships. Mr. Tory was a strategist for the Progressive Conservative before he was elected leader of the Ontario PCs, but there was an unsuccessful run for mayor in Toronto in between.