This paper presents the results from an experimental campaign to assess the three-dimensional (3D) response of masonry arch bridges under patch loads. A full-scale masonry arch bridge containing spandrel walls, an arch barrel, abutments, and backfill material was constructed. Static loads with increasing magnitudes were applied to the top of the backfill and the crack initiation and propagation recorded. The observed evolution of cracks and post-test deformations revealed a localized 3D mode of response in the arch barrel in the vicinity of the applied load and a global four-hinge mechanism. Failure-level load tests carried out sequentially at the quarter span and three-quarter span points indicated a 10% decline in the bridge’s load-carrying capacity, with a substantial reduction in stiffness of the bridge by approximately 35%. The results provide valuable insights into the behavior of masonry arch bridges, including the interaction between its constituent components. Moreover, the results presented herein can be used to calibrate both high- and low-fidelity numerical models.