As the most varied class of organic compounds, N-heterocycles—especially pyrimidine derivatives, which are found in many remarkable synthetic substances—have important chemical, biological, and industrial uses. This review sheds light on a number of techniques for building diverse fused pyrimidine scaffolds using Nheterocycle moieties as adaptable precursors. Recent studies demonstrate the promise of pyrimidine-based heterocyclic hybrids, particularly those with bicyclic (pyrido[2,3-d]pyrimidine and pyrano[2,3-d]pyrimidine) and tricyclic (pyrido[2,3-d:5,6-d0]dipyrimidine) moieties that exhibit enhanced cytotoxicity and target selectivity. Because they developed N-heterocyclic-based pyrimidine analogous frameworks in a single reaction step, multicomponent reactions are crucial in the advanced, proficient synthesis of medications. Green along with ecofriendly protocols for syntheses of such organic moieties are essential for sustainable growth of the pharmaceutical and agrochemical fields. This review highlights the structure–activity relationships guiding the advancement for next-generation pyrimidine pharmaceutical chemotypes and embraces various synthetic strategies and summarizes recent research developments, as well as reveals the many important biological characteristics (anticancer, in vitro a-amylase inhibitory, antimicrobial, antiviral, anti-inflammatory, antioxidant, antituberculosis, antidiabetic, anticholinesterase, antiplatelet, and in vitro antimalarial agents)