This paper entails the results of demineralization carried out on Karanpura Gondwana coals having high ash (30.57–21.80%) and low sulfur (0.29–0.20%) contents. The coal samples were subjected to demineralization using Pseudomonas mendocina strain B6-1, and the effect of various parameters, such as pH, temperature, incubation time, and pulp density, was observed. Optimum values of demineralization were found at pH 6.0, temperature of 35 °C, 6.0% (w/v) pulp density, and incubation time of 7 days. Reduction in the mineral matter (mean of 13.72–29.10%) content led to a relative increase in vitrinite, inertinite, and liptinite macerals. Further, the treatment has also caused an increase in the useful heat value, gross calorific value, and net calorific value of coal from 4824.86 to 5192.06 cal/g, from 5396.72 to 5647.47 cal/g, and from 5059.30 to 5273.80 cal/g (mean values), respectively. The method is eco-friendly and useful in obtaining clean fuel.