A functional polymer membrane including a porous support and a crosslinked polymer electrolyte, in which the film thickness of the functional polymer membrane is smaller than 100 μm, the crosslinked polymer electrolyte is a crosslinked polymer formed by subjecting a composition including a monomer having a (meth)acrylamide skeleton to a polymerization curing reaction, and the proportion of elemental oxygen in the elemental composition excluding elemental hydrogen and helium at the surface of the porous support is from 14.0 atom % to 25.0 atom %; and a method for producing the same are provided.