Hepacivirus is a genus of RNA viruses within the family Flaviviridae of which hepatitis C virus (HCV) is the prototype. Several hepaciviruses have been identified in mammals, including rodents of multiple families. Each rodent hepacivirus described so far has been found only in members of a single rodent species. Here, we report the discovery and characterization of a putative new genotype of an unclassified rodent hepacivirus in a wild cavy (Cavia aperea aperea) that was reported previously in Proechimys semispinosus. This virus was detected in one out of 14 (7.14%) wild cavy sera tested by RT-PCR. The complete genome sequence was obtained by high-throughput sequencing using an Illumina MiSeq platform. This is the first report of a hepacivirus in a member of the family Caviidae. Our findings show that members of different rodent species and even families can be infected by hepaciviruses of the same species. The identification and characterization of novel hepaciviruses might lead to the discovery of reservoirs of viruses that are genetically related to human pathogens, and this can help to elucidate the evolutionary origins of HCV and other hepaciviruses.