Encoding and manipulating digital information in quantum degrees of freedom is one of the major challenges of today’s science and technology. The valley indices of excitons in transition metal dichalcogenides (TMDs) are well-suited to addressing this challenge. Here, we employ mechanical strain to manipulate intervalley interactions and tune the valley polarization dynamics of excitons across a broader range of momentum space in monolayer TMDs. We use strain engineering to form valley-hybridized excitons that combine the advantages of bright intravalley excitons, where the valley index directly couples to light polarization, and dark intervalley excitons, characterized by low depolarization rates. We demonstrate that these valley-hybridized excitons exhibit signatures of coherently coupled states with a 100-fold reduction in valley depolarization rate and up to a 5-fold increase in steady-state valley polarization compared to previously studied excitons. Our findings of strain-tunable valley character of excitons advance the applications of TMDs in valleytronics.