Biohythane is typically composed of 60/30/10 vol% CH4/CO2/H2 and can be produced very efficiently from two-stage anaerobic digestion of renewable and low carbon biomass and with a greater overall energy yield compared with CH4/CO2 biogas. This work investigates the effects of fuel variability on the electrical performance and fuel processing of a commercially available anode-supported solid oxide fuel cell (SOFC) operating on biohythane mixtures. Cell electrical performance was characterised using current-voltage curves and electrochemical impedance spectroscopy. Fuel processing was characterised using quadrupole mass spectroscopy. It is shown that operating SOFCs on blends of CH4 and H2/CO2 is potentially a very effective route to the decarbonisation of natural gas grids due to increased cell electrical performance, overall efficiency and CH4 consumption savings. Enhanced electrical performance was due to promotion of CH4 dry reforming, the reverse Boudouard reaction and the additional presence of H2, which alleviated carbon deposition and promoted electrochemical oxidation of H2 as the primary power production pathway. Substituting 60 vol% CH4 with 25/75 vol% H2/CO2 increased cell power output by 66.4% at 0.7 V relative to pure CH4, and corresponded to a 3.7-fold increase in overall energy conversion efficiency and a 76% decrease in CH4 consumption. A 260 hour durability test demonstrated good cell durability when operating on 60/30/10 vol% CH4/CO2/H2 under high fuel utilisation. Overall, this work suggests that substituting natural gas with H2/CO2 mixtures rather than pure H2, and utilising in SOFC technology, gives greater gains in energy conversion efficiency and carbon emissions savings.