Abstract Mesoscale convective systems (MCSs) play a central role in producing extreme precipitation over the conterminous United States (CONUS), yet their simulation and future evolution remain elusive. Here we present a comprehensive, observation‐constrained evaluation of MCSs during 2001–2020 using multisource satellite and in situ observations, ERA5 reanalysis, high‐resolution Community Earth System Model (CESM‐HR), and a 4‐km convection‐permitting regional simulation (CONUS404). CESM‐HR faithfully simulates cold‐season MCS climatology, structure, and precipitation characteristics, with heavy precipitation dominated by resolved‐scale modeling processes. CONUS404 better captures warm‐season MCS precipitation intensity but tends to produce more compact systems. Despite differences in historical performance, both CESM‐HR and CONUS404 project intensified MCS‐related extreme precipitation, expanded spatial extent, increased frequency by the mid–twenty‐first century, indicating a robust response to warming. In contrast, projected future changes in MCSs geographic distributions and lifetime duration remain model dependent, highlighting the continued challenges in constraining the dynamical aspects of MCS evolution.