A methacrylic resin composition comprises a methacrylic resin, the methacrylic resin comprising: 50 mass % to 97 mass % of a methacrylic acid ester monomer unit (A); 3 mass % to 30 mass % of a structural unit (B) having a cyclic structure-containing main chain; and 0 mass % to 20 mass % of another vinyl monomer unit (C) that is copolymerizable with a methacrylic acid ester monomer, wherein the methacrylic resin satisfies a specific condition; and the composition has a weight average molecular weight residual ratio of 80% or more upon heating under a nitrogen atmosphere at 280° C. for 1 hour, and has a weight average molecular weight residual ratio of 80% or more upon heating in air at 280° C. for 0.5 hours.