The current study demonstrates the synergistic effect of co-gasification of high-ash Indian coal and biomass (press mud and sawdust) blends in varying proportions in a pilot-scale bubbling fluidized bed gasifier (BFBG) with a capacity of 20 kg/h. The effect of blending on product gas yield, composition and heating value, carbon conversion, and cold gas efficiency was critically analyzed. Mineralogical transformations and catalytic effects were investigated during co-gasification, wherein minerals in ash residue, such as hematite, sylvite, chlorite, K-feldspar, CaO, and MgO, showed a catalytic role in co-gasification, increasing the product gas compositions, and reverse the trend for kaolinite and phosphate minerals. Blending coal with biomass enhances the porosity and reactivity of blends, surface morphology, gasification performance, and product gas yield. So, high ash coal and biomass are suitable for gasification. The high ash coal gasification comprises the volumetric product gas composition (%) of CO (9.79), CO2 (8.75), H2(13.6), and CH4(1.12) with the maximum blends (40%) of biomass, the volumetric composition (%) is enhanced comprising CO (17.71), CO2 (14.8), H2(19.9) and CH4(2.05) for press mud blend, and CO(15.84), CO2(14.2), H2(18.3) and CH4(2.29) for sawdust blend, respectively, and HHV increases from 3.42 (MJ/Nm3) to 5.59(MJ/Nm3).