Merhi made the full-time step-up to Formula Three in 2009 when he was signed by Manor Motorsport for their Formula 3 Euro Series campaign, finishing seventh, with four podiums.
Merhi disputou a tempada completa de Fórmula Tres en 2009, cando asinou por Manor Motorsport para facer a campaña de Fórmula 3 Euro Series, terminando sétimo , con catro podios.