Sustainable disposal techniques of municipal solid wastes (MSW) are essential for effective materials recovery and energy management. Synergistic incorporation of gypsum waste from the construction and demolition (C&D) sector is explored here for the low techno-economic viability of MSW in waste-to-energy facilities. Co-processing of MSW with this low-value gypsum can potentially provide improved product recovery and simultaneously furnish economic viability. To understand the impact of gypsum incorporation into MSW conversion, we tested synthetic MSW and a 1:1 mixture of MSW with gypsum from drywall wastes and compared their micro-scale mass loss kinetics along with macro-scale syngas evolution and conversion at different temperatures, and in pyrolytic and oxidizing environments. Gypsum incorporation led to increased syngas production and decreased char yields as the char was oxidized by CaSO4. Thermogravimetric analysis (TGA) revealed two different temperature zones of gypsum interaction with MSW depending on the oxidation concentration in the environment. Adding 50% gypsum only changed the final ash yield by 10% in pyrolysis conditions suggesting the viability of gypsum incorporation. While the addition of gypsum led to delayed evolution of H2 and CO, the cumulative yields of H2 and CO2 increased significantly and the yield of CO changed minimally. Additionally, hydrocarbon by-products such as CH4 decreased by gypsum addition. The results showed improved syngas yield and uniformity, as well as operational conditions from the gypsum interaction with MSW which can help in the further development of gypsum waste incorporation.