Saussurea costus is rich in numerous aromatic functional groups containing polyphenolic compounds, which possess a wide range of biological properties. The present study focused on utilizing S. costus extract for the green synthesis of gold nanoparticles (Au-NPs), which were subsequently used for in vitro biological activities. The extraction process involved the use of 3 different solvents. It was observed that the methanolic S. costus extract had the highest concentration of major phyto-constituents, and consequently, demonstrated the highest in vitro biological activities. Consequently, it was chosen for the biosynthesis of the Au-NPs, which were characterized using various instrumental techniques. The incorporation of Au-NPs enhanced the biological efficiency compared to the native methanolic extract. Moreover, the gold S. costus nano-extract exhibited the lowest median inhibitory concentration (IC50) against human hepatocellular carcinoma (HepG2) cell lines. Treatment of the HepG2 cells with the nano-extract ameliorated the expression of apoptotic genes (EGFR, Bcl-2, and Casp3) compared to the native extract. Furthermore, the gold nano-extract was safer than the native extract when administered orally, as evidenced by the highest median lethal (LD50) and therapeutic doses. The study concluded that the in vitro biological activities and safety of the methanolic S. costus extract increased after incorporating Au-NPs compared to the native extract.