This paper presents the results of our ab initio study of energy configurations, minimum energy path (MEP), and migration energy for neutral indium diffusion in a uniaxially and biaxially tensile-strained {l00} silicon layer. Our ab initio calculation of the electronic structure allowed determination of the transient atomic configurations during indium diffusion in strained silicon. We found that the lowest energy structure (InS-${Si_i}^{Td}$) consists of indium located on a substitutional site while stabilizing the silicon self-interstitial in a nearby tetrahedral position. Our ab initio calculation implied that the next lowest energy structure is ${In_i}^{Td}$, the interstitial indium at the tetrahedral position. We used the nudged elastic band method to estimate the MEP between the two structures. Or results indicated that the diffusion pathway of neutral indium remains unchanged, while the migration energy of indium fluctuates in strained silicon.