Ascorbate (vitamin C) is a powerful antioxidant and scavenger of free radicals that protects plants against oxidative damage caused by adverse environmental conditions such as drought, salt stress, and herbicide use. Dehydroascorbate reductase (DHAR; EC 1.8.5.1) and monodehydroascorbate reductase (MDAR; EC 1.6.5.4) are crucial for ascorbate regeneration and the maintenance of a pool of the reduced form. In this study, we report the development of transgenic potato (Solanum tuberosum L.) that overexpresses the Arabidopsis thaliana DHAR gene (AtDHAR1) in the cytosol. The transgenic plants exhibited up to 4.5 times the DHAR activity and up to 2.8 times the level of reduced ascorbate found in the wild-type plants. When subjected to methylviologen treatment, the transgenic plants exhibited enhanced tolerance in terms of less ion leakage, greater chlorophyll contents, less accumulation of hydrogen peroxide, and less severe visual injury symptoms. Moreover, the transgenic plants exhibited faster growth under drought and salt stress. Our results demonstrate that elevating ascorbate contents by overproducing DHAR represents a viable approach for the development of herbicide-tolerant potato.