Congo red (CR) is a synthetic azo dye commonly used in the textile and printing industries. However, CR is also a known pollutant that can cause environmental and health problems. This study investigates the use of Ag-NiO@g-C3N4 nanocomposite as an adsorbent for the removal of CR from aqueous solutions. The Ag-NiO@g-C3N4 nanocomposite was synthesized via a facile ultrasonication method followed by thermal annealing. The synthesized nanocomposite was characterized by TEM, EDX, XPS, BET, XRD and an FT-IR spectrometer. The synthesized nanocomposite exhibited a high surface area of 94.705 m2/g. The adsorption performance of the Ag-NiO@g-C3N4 nanocomposite towards CR dye was investigated under various operational parameters, including pH, initial CR dye concentration, and contact time. Comparative studies with other dyes, namely basic fuchsin (BF), crystal violet (CV), Methylene blue (MB), Rhodamine 6G (RG), and other mixed dyes were also conducted. The adsorption of CR dye onto the Ag-NiO@g-C3N4 nanocomposite was found to follow the pseudo-second-order kinetic model and the Langmuir isotherm, suggesting monolayer adsorption with a finite number of binding sites. The maximum adsorption capacity of the Ag-NiO@g-C3N4 nanocomposite for CR dye was 229.48 mg/g. The results of this study demonstrate the potential of the Ag-NiO@g-C3N4 nanocomposite as an effective adsorbent for CR dye removal from wastewater.