Abstract Aseismic slip has been observed on many active faults globally, but its controlling mechanisms remain unclear. This study focuses on the NW‐striking, left‐lateral Katouna‐Stamna Fault in Western Greece. We use InSAR surface deformation measurements to confirm the presence of aseismic slip and compare this behavior with structural evidence from field observations. We measure sharp velocity changes across the fault, up to 2 mm/yr in the satellite’s ascending and 4 mm/yr in the descending Line‐Of‐Sight. Kinematic modeling indicates strike‐slip rates of up to 19± $pm $1 mm/yr, with pure left‐lateral slip in the south‐central part of the fault transitioning to oblique slip with a normal component in the north. Field data indicate a switch from WNW‐ to NNW‐directed transtension over time. Ductile gypsum deformation suggests that fluids and pressure‐solution creep could play a key role in the aseismic fault behavior.