Biomethane production by anaerobic digestion can significantly contribute to the decarbonation and defossilization of the European energy mix. Although previous estimates have been provided about biomethane potential production in several European countries, they suffer from a coarse evaluation of substrate availability and a lack of spatial resolution. This paper provides a spatially-explicit assessment of the potential for biomethane production in France at a fine spatial resolution (NUTS 4 region) from agricultural biomass (livestock manure, crop residues and cover crops) and sewage sludge. This assessment is based on (i) a fine estimation of substrate availability, particularly for cover crop production, by combining a crop model with spatially-explicit soil and climate databases; (ii) the use of an anaerobic digestion model that predicts biomethane production from agricultural biomass; and (iii) a procedure for optimizing biomethane production while respecting the stoichiometric constraints of the substrate mixture. We found a significant potential for annual biomethane production of 64.1 TWh, mainly from cattle manure, a value that could reach 108.7 TWh through the generalization of cover crops within arable cropping systems. Our results also highlighted the importance of detailed substrate availability data to account for their large spatial variations. Accordingly, we showed that biomethane production was highly variable across the French regions and that crop residues could only partly be used for anaerobic digestion - especially in arable regions - because they lead to excessively dry substrate mixtures. This study helped to identify the most suitable regions for biomethane production and to provide accurate estimates for biomethane development in France.