A driver assist system for a vehicle includes a plurality of vehicle cameras and at least one trailer camera, with the vehicle cameras configured to be disposed at a vehicle and having respective fields of view exterior of the vehicle and the trailer camera configured to be disposed at a trailer towed by the vehicle. An image processor is operable to process image data captured by the vehicle cameras and the trailer camera. Responsive to processing of captured image data during forward or rearward motion of the vehicle and trailer, the image processor is operable to calibrate the trailer camera with the vehicle cameras. Responsive to processing of captured image data during forward or rearward motion of the vehicle and trailer, the image processor is operable to determine objects rearward of the trailer that are not in the fields of view of the vehicle cameras.