It has been well established that the metabolism of T cells is integral to their functionality. If a T cell cannot generate enough energy or building blocks, it will not be able to exert its cytotoxic properties to eliminate pathogens and cancer cells. Impairment of mitochondrial oxidative phosphorylation is a well-known disruptor of T cell activation. Dihydroorotate dehydrogenase (DHODH) is a rate-limiting component of the de novo synthesis of pyrimidines and its activity is dependent on functional mitochondrial oxidative phosphorylation. In this regard, DHODH inhibitors have long been used in clinical settings for the treatment of autoimmune diseases, as they potently inhibit lymphocyte proliferation. The exact mode-of-action of these inhibitors in T lymphocytes is not yet exactly understood. In this review, we briefly discuss the critical role of mitochondria in T cell functionality. We also describe how de novo pyrimidine biosynthesis is linked to mitochondrial activity. Finally, we summarize our current knowledge of how mitochondrial-linked de novo pyrimidine biosynthesis modulates T cell responses.