While it is well established that CD8⁺ T cells generated in the absence of CD4⁺ T cells mediate defective recall responses, the mechanism by which CD4⁺ T cells confer help in the generation of CD8⁺ T‐cell responses remains poorly understood. To determine whether CD4⁺ T‐cell‐derived IL‐21 is an important regulator of CD8⁺ T‐cell responses in help‐dependent and ‐independent viral infections, we examined these responses in the IL‐21Rα^−/− mouse model. We show that IL‐21 has a role in primary CD8⁺ T‐cell responses and in recall CD8⁺ T‐cell responses in help‐dependent viral infections. This effect is due to a direct action of IL‐21 in enhancing the proliferation of virus‐specific CD8⁺ T cells and reducing their TRAIL expression. These findings indicate that IL‐21 is an important mediator of CD4⁺ T‐cell help to CD8⁺ T cells.