Natural killer (NK) cells are key regulators of innate defense against mouse cytomegalovirus (MCMV). Like NK cells, NKT cells also produce high levels of IFNγ rapidly after MCMV infection. However, whether similar mechanisms govern activation of these two cell-types, and the significance of NKT cells for host resistance, remain unknown. Here we show that although both NKT and NK cells are activated via cytokines, their particular cytokine requirements differ significantly, in vitro and in vivo. IL-12 is required for NKT cell activation in vitro, but is not sufficient, while NK cells have the capacity to be activated more promiscuously in response to individual cytokines from innate cells. In line with these results, GM-CSF-derived DC activated only NK cells upon MCMV infection, consistent with their virtual lack of IL-12 production, while Flt3L-derived DC produced IL-12 and activated both NK and NKT. In vivo, NKT cell activation was abolished in IL-12−/− mice infected with MCMV, while NK cells were still activated. In turn, splenic NK cell activation was more IL-18 dependent. The differential requirements for IL-12 and IL-18 correlated with the levels of cytokine receptor expression by NK and NKT cells. Finally, mice lacking NKT cells showed reduced control of MCMV, and depleting NK cells further enhanced viral replication. Taken together, our results show that NKT and NK cells have differing requirements for cytokine-mediated activation and both can contribute non-redundantly to MCMV defense, revealing that these two innate lymphocyte subsets function together to fine-tune antiviral responses.