Lithium stannate (Li2SnO3) is currently being considered as a material for electrode and electrode coating applications in Li-ion batteries. The intrinsic defect formation and Li-ion transport properties of Li2SnO3 doped with divalent and trivalent transition-metal dopants Mn, Fe, Co, and Ni) are explored in this work using atomistic simulations. Defect formation simulations reveal that all divalent dopants occupy the Li site with charge compensation through Li vacancies. For trivalent doping, occupation of the Sn site is energetically preferred with charge compensation from Li interstitials. Molecular dynamics simulations reveal that divalent and trivalent dopants increase Li-ion diffusion and reduce its activation energy compared with the undoped system. We show that Li2SnO3 with Li excess or deficiency as a result of doping has improved Li-transport properties. This study highlights the substantial improvement in Li-ion diffusion of Li2SnO3 for both current commercial and next-generation that can be achieved through transition-metal doping.