Fire poses a major threat to structures worldwide, particularly to steel structures, due to the well-known deterioration of steel strength at elevated temperatures. Among structural components, connections play a crucial role in transferring forces between load-bearing members, and their failure during fire can compromise the entire structural system. Despite this critical role, the high-temperature behavior of connections under fire conditions has been relatively underexplored. This paper presents a comprehensive numerical study on the thermo-mechanical response of bolted end-plate moment connections in steel frames subjected to fire. Nonlinear three-dimensional finite element models were developed and validated against experimental data to examine connection failure modes, mid-span beam deflection, and axial forces under elevated temperatures. The validated models were then used to perform parametric analyses to investigate the effects of beam length and end-plate thickness on the connection performance. The findings reveal that longer beam spans lead to failure at lower temperatures, with axial forces peaking and diminishing more rapidly as the temperature increases. Additionally, thicker end plates reduce bolt tensile forces and shift the dominant failure mechanism from the connection region to the beam itself.