A thermosetting resin composition, a thermosetting resin composition for protective films, a thermosetting resin composition for planarizing films, and a method for producing a cured film, a protective film, or a planarizing film by using the resin composition. A thermosetting resin composition has a polymer having a structural unit of Formula (1) below, a curing agent in an amount of 0% by mass to 30% by mass with respect to the polymer, and a solvent. When the thermosetting resin composition includes the curing agent, the curing agent is at least one compound selected from polyfunctional (meth)acrylate compounds and polyfunctional blocked isocyanate compounds: (wherein A1 is a C2 or C3 alkenyl group or alkynyl group, and A2 is a C2 alkenylene group or alkynylene group).