In recent years, plasma-induced non-equilibrium electrochemistry (PiNE) has been increasingly used for the synthesis of nanomaterials. In this study, we investigated the effect of solution pH on the formation of AuNP/MWCNT nanocomposites synthesized by PiNE. It is found that resulting nanocomposite morphology can be manipulated by the solution pH with pH 2 giving the most uniformly distributed AuNP along the MWCNT surface during the nanocomposite formation. The detailed mechanisms of AuNP/MWCNT nanocomposites formation under different pH have been discussed. For selected AuNP/MWCNT, we further evaluated the photothermal conversion performance under a blue laser (wavelength 445 nm) and the material biocompatibility using HeLa cells. The promising photothermal capability and biocompatibility of the composite sample point to their potential future applications such as solar thermal conversion and healthcare technology.