The identification of KRASG12C inhibitors has reignited interest in targeting RAS proteins. This work describes the discovery of the KRASG12D-specific inhibitor MRTX1133 and demonstrates the feasibility of potently and selectively targeting this oncogenic variant. MRTX1133 treatment markedly inhibited KRAS-dependent signaling and induced tumor regression in xenograft models harboring the KRASG12D mutation.