The widespread usage of pharmaceutical compounds for treating humans and animals has led to substantial environmental harm to living organisms globally. Herein, the engineering of step-scheme (S-scheme) heterojunction composite incorporating a co-adsorbent agent is garnering attention as a promising approach for environmental remediation, owing to its improved redox potential and expanded active surface area. This study is the first to employ a graphene-integrated MgO/WO3 S-scheme heterostructure (denoted as MWG) as a ternary photocatalyst for the disintegration of tetracycline (TCY) under UV light exposure. The results confirmed that the MWG nanocatalyst exhibited a significantly improved photocatalytic activity in the degradation of TCY when contrasted with pure MgO, WO3, and graphene (GRP) nanomaterials. Kinetic investigation elucidated that the detoxification of TCY under optimized circumstances was best described by a pseudo first-order kinetic model with regression coefficients higher than 0.97. The scavenging tests revealed that HO● species are the primary agents involved in the TCY degradation during the photocatalytic process. Trapping experiments, photoelectrochemical techniques, and band structure analysis were conducted to propose the plausible detoxification mechanism via the MWG/UV process. A notable enhancement in the biodegradability of actual wastewater was attained following treatment with the MWG/UV process, resulting in 79.6% and 64.8% COD and TOC elimination, respectively, over a 200 min of reaction time. To sum up, the employment of a graphene-integrated MgO/WO3 S-scheme heterojunction composite under UV light illumination can be considered a novel and effective approach for the remediation of real pharmaceutical effluents in real-world scenarios, attributable to its robust redox capacity, significant stability, economic viability, and heightened efficacy in degradation/mineralization processes.