Myxoma virus (MV) is a candidate for oncolytic virotherapy due to its ability to selectively infect and kill tumor cells, yet MV is a species-specific pathogen that causes disease only in European rabbits. To assess the ability of MV to deliver cytokines to tumors, we created an MV (vMyxIL-12) that expresses human interleukin-12 (IL-12). vMyxIL-12 replicates similarly to wild-type MV, and virus-infected cells secrete bioactive IL-12. Yet, vMyxIL-12 does not cause myxomatosis, despite expressing the complete repertoire of MV proteins. Thus, vMyxIL-12 exhibits promise as an oncolytic candidate and is safe in all known vertebrate hosts, including lagomorphs.