Cemented paste backfill (CPB) is a key material in underground mining, providing essential ground support while aiding in tailings management. However, current research has overlooked the combined effects of horizontal rockwall closure stress and vertical self-loading stress, referred to as multiaxial stress, on the CPB's consolidation behavior and its mechanical properties development. Understanding and assessing these effects is critical because they directly affect the stability and performance of CPB structures. In this study, a novel multiaxial compressive stress curing and monitoring apparatus was used to simulate two horizontal rockwall closure scenarios with a consistent backfilling rate, under both drained and undrained conditions. Key parameters assessed included unconfined compressive strength (UCS), deformation during curing, stress-strain behavior, and modulus of elasticity. The results highlight that rockwall closure, combined with vertical stress, plays a pivotal role in the consolidation behavior of CPB, significantly affecting key mechanical properties. Higher horizontal stress from faster rockwall closure intensified compression during curing, leading to reduced porosity, enhanced particle rearrangement, and accelerated consolidation. This intensified consolidation leads to notable improvements in mechanical properties, including increased UCS, enhanced stiffness, and a higher modulus of elasticity, indicating improved load-bearing capacity. Moreover, the interaction between multiaxial stress and drainage conditions influenced stress-strain behavior and deformation, with drained conditions promoting earlier plasticity and higher peak stresses. These findings underscore the critical influence of multiaxial stress, combined with drainage conditions, on CPB performance, offering valuable insights for optimizing CPB design in underground mining applications.