The large DNA viruses, cytomegalovirus and herpes simplex virus, evade the host defense pathways by expressing inhibitors of the host apoptosis and necroptosis programmed cell death pathways. In murine cytomegalovirus, the protein M45 inhibits host necroptosis and allows latent infection with the virus. In herpes simplex virus, the protein ICP6 plays a similar role. We show that the RIP homotypic interaction motif (RHIM) within these proteins renders them amyloidogenic and that M45 and ICP6 RHIM-containing domains form homomeric amyloid fibrils with hallmark physical characteristics. Additionally, we have used a wide range of biophysical techniques, including single molecule fluorescence studies, to demonstrate that these proteins are able to form heteromeric amyloid fibrils through co-assembly with the receptor interacting kinases RIPK1 and RIPK3 which each contain RHIMs. RIPK1 and RIPK3 have previously been shown to form a functional heteroamyloid complex that signals for cell death by necroptosis. The viral proteins display different affinities for RIPK1 and RIPK3 and form heterofibrils that are more stable than the homomeric amyloid-based complexes. Our results demonstrate that the ability of the viral proteins M45 and ICP6 to form competing “decoy” amyloid fibrils with RIPK1 and RIPK3 underlies suppression of RIP-induced programmed necroptosis by these viruses.