This paper proposes and examines an alternative thermo-chemical process for biomethane production from lignocellulosic biomass, termed self-gasification. Self-gasification of biomass is envisaged to utilize a high-pressure steam gasifier (30−80 bar) at temperatures of 600−900 °C and to use the alkali metals in biomass as gasification and methanation catalysts. The concept was studied by performing preliminary process simulations and by several screening experiments with wood. The simulations gave insight into the effect of gasifier operating conditions on methane yield. After screening tests of different alkali metals, KOH was chosen as a model compound for biomass-derived ash for further experimentation. It improves char reactivity by more than an order of magnitude, and thermogravimetric data interpreted by a first-order reaction model showed that it accelerates the pyrolysis reaction reducing the activation energy from Ea = 143 kJ/mol to Ea = 65 kJ/mol. Methane amounts higher than dictated by equilibrium are produced with and without impregnated KOH.