The firm, which also owns luxury bike maker Buell, is looking for an agency to co-ordinate its consumer work across key regions - complementing its UK agency, which it hired in January.
RBP was brought in to handle press comms and model launches.
There is no Europe-wide agency currently in place. Harley-Davidson is planning to significantly expand its dealer network through 2007.
This follows a trend-busting 2006 which saw an 11 per cent increase in sales (compared with a motorcycle market increase of one per cent).