A copper–molybdenum–phosphate (CuMoP)-modified screen-printed carbon electrode (SPCE) was developed (mSPCE) via one-step potentiostatic codeposition for the electrochemical detection of aspirin (acetylsalicylic acid, ASA). Microscopic and spectroscopic analyses confirmed a uniform, granular CuMoP film with mixed-valence Cu+/Cu2+and Mo6+centers coordinated by phosphate groups, thereby enhancing electron–proton coupling. The sensor exhibited a well-defined irreversible oxidation peak at 0.866 V (pH 3.0), showed highly sensitive detection for ASA, and followed a diffusion-controlled two-electron mechanism. Differential pulse voltammetry revealed an excellent linear response (I = 0.036 + 0.012 C,R2 = 0.9979) over 2.0–92.6 µM, with a limit of detection of 1.5 µM and a quantification limit of 5.0 µM. The mSPCE displayed high stability (RSD = 2.6%), reproducibility (RSD = 5.4%), and recovery of 91.21%–103.52% for pharmaceutical tablets. Outstanding selectivity against 100-fold interfering species highlights the synergistic Cu–Mo–P redox network as an efficient, low-cost, and portable platform for sensitive determination of ASA in real samples.