Photodynamic therapy (PDT) and photothermal therapy (PTT) are promising tumor treatment modalities which employ light activation to acquire high temperature and reactive oxygen species (ROS) for the annihilation of cancer cells. In this study, a bilirubin (BR)-gold nanoconjugate (BGNC) was synthesized, characterized, and analyzed as a photosensitizer for synergistic PTT/PDT of HeLa cancer cells. BGNC contained nanoparticles with an average diameter of 33 nm, a zeta potential of -18.6 mV, a band gap energy of 2.7 eV, and a photothermal conversion efficiency of 51.6%, with an intrinsic ROS-generating efficiency. BGNC benefits from the surface plasmon resonance (SPR) and ROS-producing properties of gold nanoparticles, and antioxidant and glutathione (GSH)-reducing properties of BR. Concentration-dependent effects for BGNC in decreasing Hela cell viability were assessed. Hela cell viability further lowered upon 808-nm laser light irradiation of BGNC. The ability of BGNC to generate ROS upon irradiation was confirmed in cell-free as well as cell-containing systems, with a 2.1-fold increment in intracellular ROS in treated cells with BGNC and light irradiation. BGNC also exhibited a concentration-dependent effect to deplete the GSH level. BGNC acted as a two-pronged photosensitizer agent, exhibiting enhanced anticancer efficacy by leveraging both phototherapy and the intrinsic properties of BR.