A convenient synthetic route was developed for the preparation of structurally diverse quinazolinone–thiazole hybrids using a common thiosemicarbazide intermediate (2), which underwent cyclization with different electrophiles to afford three series of derivatives (4a–e/6, 8a–c, and 11a,b/13). The structures of all synthesized compounds were confirmed by IR, NMR, MS, and elemental (CHN) analyses. The cytotoxic activity of the obtained compounds was evaluated against HCT‐116 human colon cancer cells using the MTT assay after 24 h of incubation. Compounds 4b (IC50 = 3.82 µM), 4a (IC50 = 4.07 µM), and 11b (IC50 = 4.09 µM) were the most active derivatives, showing activity comparable to doxorubicin (IC50 = 4.17 µM), while compound 6 also showed good activity (IC50 = 5.92 µM). Preliminary structure–activity relationship analysis indicated that electron‐donating aryl substituents such as methyl and methoxy groups enhanced the activity in the 4‐series, whereas electron‐ withdrawing substituents such as chloro, bromo, and nitro reduced it; in the 11‐series, the ethyl ester derivative 11b was more potent than the corresponding acetyl derivative 11a. Cytotoxicity against the non‐tumor LLC‐MK2 cell line showed that compounds 4a, 4b, 6, and 11b exhibited IC50 values > 100 µM, indicating a favorable preliminary selectivity toward the cancer cell line. Molecular docking against human uridine 5′‐monophosphate synthase (UMPS, PDB: 7OUZ) supported the observed activity trends, and in silico ADMET prediction suggested acceptable drug‐like and pharmacokinetic properties. Overall, compounds 4a, 4b, and 11b emerged as promising anticancer candidates for further mechanistic and selectivity studies.