The calculated distance (air line) between Saint-Mitre-les-Remparts and Marseille is approximately 21 miles respectively 34 kilometers.
By car or train, the actual journey to Marseille is certainly longer, as only the direct route (as the crow flies) between Saint-Mitre-les-Remparts and Marseille has been calculated here.
Air line (approximately)
34 kilometers
19 nautical miles