Fused pyrimidines are a class of heterocyclic compounds that have gained considerable interest due to their extensive biological activities and potential applications in drug development. This review article aims to provide a comprehensive overview of the latest synthetic approaches to fused pyrimidines, including Michael reactions, multicomponent reactions, metal‐catalyzed reactions, photocatalytic reactions, peroxide‐mediated reactions, and inverse electron demand Diels–Alder reactions. Furthermore, the biological activities of these compounds, such as their ability to combat cancer and microbial infections, are also discussed. This review article summarizes the existing literature on the synthesis and biological activity of fused pyrimidines from 2020 to 2023. We hope this review article will inspire the development of more effective and less toxic fused pyrimidine drugs with well‐designed structures. [ABSTRACT FROM AUTHOR]