Rammed earth walls show comparatively good performances with respect to vertical loads, while their stiffness and strength against horizontal loads are often unsatisfactory. Preliminary indications about the timber-framed rammed earth panel (TREP) stiffness and load bearing capacity have been obtained from a first experimental study that has been expressively set up and performed to investigate the TREP in-plane static behavior. The present part I, together with the subsequent part II (companion paper), illustrates and discusses the key experimental results obtained from the compression-shear loading tests performed on rammed earth panels reinforced by a contouring timber frame. In the present part I of the paper, the monotonic loading tests are carefully analyzed, the results are discussed, and the detected damage modes are explained. The results seem to show that the reinforcing timber frame provides a substantial benefit enabling the development of an effective “strut-and-tie” resisting mechanism that effectively exploits the compressive strength of the rammed earth panel and promotes a ductile failure mode.