CRISPR/Cas systems, initially characterized as bacterial adaptive immune mechanisms, have rapidly emerged as precise and versatile genome-editing tools with significant potential for antiviral research and therapeutic development. This review highlights the role of CRISPR/Cas systems in targeting persistent and human oncogenic viruses, including HPV, HBV, HCV, EBV, KSHV, HTLV-1, and MCPyV, as well as HIV, which may indirectly contribute to cancer through immune dysregulation. Many of these viruses can integrate into the host genome or persist as chronic or latent infections, contributing to cancers for which curative options are limited. CRISPR-based strategies enable the excision of integrated proviral DNA, disruption of viral replication, targeted silencing of viral transcripts, and modulation of host tumor-suppressor pathways. Cas9 efficiently targets DNA viruses, such as HBV and HPV, whereas RNA-targeting Cas13 allows precise silencing of RNA viruses, like HCV. Editing T-cell receptors, including CCR5 and CXCR4, offers the potential for long-term resistance to HIV. CRISPR-based preclinical studies indicate the potential to disrupt HBV cccDNA, suppress EBV and KSHV latency gene expression, and inactivate HTLV-1 oncogenes, thereby potentially reducing viral persistence and oncogenic progression. Despite these advances, challenges remain regarding off-target effects, delivery efficiency, immune responses, and ethical considerations. Innovations such as high-fidelity Cas variants, base and prime editing, and non-viral delivery systems are expected to enhance both safety and therapeutic precision. This review provides an overview of viral life cycles, oncogenic pathways, and therapeutic vulnerabilities of human oncogenic viruses and CRISPR-based genome-editing approaches under investigation for viral elimination and cancer therapy.