The catalytic activity of a wood char towards CH4 decomposition in a pyrolysis gas was investigated in a fixed bed reactor for maximising hydrogen production from biomass gasification. Wood char is suggested to be the cheapest and greenest catalyst for CH4 conversion as it is directly produced in the pyrolysis facility. The conversion of methane reaches 70% for a contact time of 120 ms at 1000 °C. Because steam and CO2 are simultaneously present in the pyrolysis gas, the carbon catalyst is continuously regenerated. Hence the conversion of methane quickly stabilises. Such a phenomenon is shown to be possible through the oxidation of the char by CO2 and H2O at high temperature, which prevents the blocking of the mouth of pores by the concurrent pyrolytic carbon deposition. In the experimental conditions, oxygenated functional surface groups are continuously formed (by steam and CO2 oxidation) and thermally decomposed. The active sites for CH4 chemisorption and decomposition are suggested to be the unsaturated carbon atoms generated by the evolution of the oxygenated functions at high temperature.