The calculated distance (air line) between Port-Saint-Louis-du-Rhône and Marseille is approximately 29 miles respectively 46 kilometers.
By car or train, the actual journey to Marseille is certainly longer, as only the direct route (as the crow flies) between Port-Saint-Louis-du-Rhône and Marseille has been calculated here.
Air line (approximately)
46 kilometers
25 nautical miles