Waste coal tar pitch is a carcinogenic substance but it can be turned into an environmentally safe and high-value electrode material when it is pyrolyzed at high temperatures. In this study, carbonized coal tar pitch (CTP)-based electrode material was first prepared using an eco-friendly green chemistry approach. Gold nanorods (AuNRds) were then attached to CTP with 4-aminothiophenol junctions by self-assembled monolayers. AuNRds-terminated carbonaceous material was characterized with microscopy and spectroscopy techniques. The nanocomposite material was modified on a glassy carbon electrode by drop coating under an infrared lamp. An analytical method for the determination of 5-HT was developed on the new carbonaceous electrode using differential pulse voltammetry. The prepared sensor exhibited a limit of detection of 0.03 μM (S/N = 3) with a linear range from 0.5 to 10 μM and shows good reproducibility and stability. Finally, real sample tests have been successfully applied to measure 5-HT in human serum to demonstrate the feasibility of the proposed sensing platform.