Pyrolytic characteristics of three different organic solid wastes, municipal solid waste (MSW), digested MSW (DMSW), and digested swine manure (SWD), were investigated at heating rates of 10, 15, and 20 °C min^–1 in a thermogravimetric analyzer coupled with mass spectrometer. Three stages of devolatilization, dehydration (0–200 °C), decomposition of major structural components (200–500 °C), and decomposition of solid residue (500–800 °C), appeared during the pyrolysis of all the samples. The major devolatilization stage (stage II) is characterized with three peaks at 319, 379, and 438 °C for MSW, two peaks at 339 and 430 for DMSW, and one peak with a shoulder on the right at 332 and 444 °C for SWD, respectively. The evolved gas species were quantified by using a semiquantitative approach, and H₂, CO and CO₂ were noticed to be predominant gas species in the above-mentioned range. While the evolution of H₂ is mostly temperature dependent, the evolution of CO and CO₂ occurred all through the run. Isoconversional methods along with compensation effect and master plots were used to determine the kinetic triplet for the pyrolysis process. The mean activation energies were 172.02–172.3, 202.21–202.55, and 213.84–215.22 kJ mol^–1, while the pre-exponential factors were 1.81 × 10¹⁰, 1.04 × 10¹⁸, and 2.26 × 10¹⁹ for MSW, DMSW, and SWD, respectively.