In this work, a novel electrochemical sensor was designed for the simultaneous detection of dopamine (DA) and sulfadiazine (SD) using a carbon paste electrode modified with a synthesized heterocyclic azo dye, 4-((2-hydroxy-3-methylphenyl) diazenyl)-N-(pyridine-2-yl) benzenesulfonamide (HMP). The HMP dye was prepared via a diazotization–coupling process, and its structure was confirmed by appropriate spectroscopic analyses. Electrochemical studies showed that the HMP-modified electrode (HMP/MCPE) exhibited enhanced electrochemical performance, enabling accurate, simultaneous quantification of both analytes with low detection limits, along with good reproducibility and stability. Experimental parameters such as pH, scan rate, and concentration were carefully optimized to enhance sensor response. In addition, the applicability of the HMP dye was explored in forensic investigations, where it effectively developed latent fingerprints, clearly revealing Level I and Level II ridge characteristics under both normal and ultraviolet light.