Catalysts containing Ni and/or Co supported by Mg-Al were prepared using impregnation and co-precipitation methods. They were firstly evaluated for hydrogen production via supercritical water gasification (SCWG) of lignin. The effects of preparation method, active metal, and catalyst loading were studied. The identified best catalyst was then evaluated using other biomass including cellulose, wheat straw, timothy grass, and canola meal. The results reveal that Ni-Co combination is better than either Ni or Co as active metals to achieve optimum hydrogen yield. Also, co-precipitation method is better than impregnation method for the catalyst preparation. The coprecipitated CopCat-Ni2Co4 catalyst showed highest hydrogen yield from SCWG of lignin and showed decent hydrogen yield from various biomass feedstocks. The maximum hydrogen yield of 3.94 mmol/g was observed with SCWG of canola meal using the CopCat-Ni2Co4 catalyst. The results suggest that CopCatNi(2)-Co-4/Mg-Al catalyst is a flexible and capable catalyst for hydrogen production from the SCWG of biomass. [GRAPHICS] .