Corgi was bought by toy giant Hornby in April this year for £7.5million. The PR company has been brought in to initially tell collectors that the brand is still trading.
The agency will target collectors and people with an interest in classic cars and aviation as part of the brief.
The appointment follows work Threepipe does for Hornby's other brands including Scalextric and Airfix.
The work will also include promoting a forthcoming BBC2 documentary, which has been tracking the Corgi team following the acquisition.