A method of producing a biodegradable and compostable container or packaging article is described, wherein the method only employs agricultural and/or food by-products and waste as the starting material. The method according to the invention comprises a step of mixing a biomass of agricultural and/or food by-products and waste characterized by a particle size smaller than or equal to 600 microns with a plasticizer in the presence of water vapor, thereby obtaining a plastic and deformable mass, and a step of molding the mixture thus obtained into a predetermined shape by thermoforming. The method of the present invention allows a biodegradable and compostable container or packaging article having a biodegradation percentage greater than or equal to 97% to be obtained.