Pyrolysis technology holds significant potential for the harmless, resource-efficient, and reduced-volume disposal of sludge in pulp and paper mills. Currently, the understanding of the thermal behavior, thermodynamic characteristics, and product composition during the pyrolysis process of sludge from pulp and paper mills remains incomplete. In this study, thermogravimetry-Fourier transform infrared (TG-FTIR) technology was employed to investigate the thermal behavior and real-time release characteristics of volatile products during the pyrolysis of pulp and paper mill sludge pyrolysis at different heating rates. Additionally, pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS) was applied to analyze the detailed chemical composition of condensable pyrolysis products. A deconvolution approach combined with a multi-component parallel reaction kinetics model, kinetic compensation effect, and master plot method was applied to obtain detailed kinetic parameters of organic matter in the sludge. The results indicated that the pyrolysis of pulp and paper mill sludge proceeded through three main stages: drying, organic matter decomposition, and CaCO3 decomposition. Organic matter decomposition occurred primarily between 140 and 600 °C, accounting for 23.62% of the mass loss, while CaCO3 decomposition occurred between 600 and 900 °C, contributing 24.04% of the mass loss. CaCO3 decomposition produced CO2, which further reacted with pyrolytic carbon to form CO. The deconvolution analysis divided the organic matter into four pseudo-components, whose pyrolysis processes could be effectively described by the parallel reaction kinetics model. The calculated average apparent activation energies of the four pseudo-components were 171.54, 179.50, 192.05, and 200.86 kJ/mol, and the pre-exponential factors ranged from 1.74×1011 to 8.34×1016, 1.47×1011 to 5.55×1013, 1.40×1011 to 1.55×1012, and 1.67×1010 to 1.34×1013 s-1, respectively. The master plot analysis demonstrated that each pseudo-component exhibited distinct kinetic behaviors, with the reaction mechanisms shifting progressively as the conversion fraction (α) increased. For pseudo-component 1, the initial pyrolysis stage (α< 0.25) followed a three-dimensional diffusion model, gradually shifting to a reaction order model. Pseudo-component 2 followed a reaction order model at 0.10 < α < 0.55, transitioning to a diffusion model at α > 0.55. Pseudo-component 3 followed a random nucleation and growth model at 0.10 < α < 0.20, exhibiting increasing complexity at higher conversion, where the experimental and theoretical master plots no longer coincided. Pseudo-component 4 followed a reaction order model throughout the entire pyrolysis process. The effect of heating rate on the reaction mechanism was insignificant. TG-FTIR analysis identified H2O, CH4, CO2, CO, NH3, ketones, aldehydes, carboxylic acids, phenols, ethers, and aromatic compounds as major pyrolysis products. Py-GC/MS further revealed that styrene (28.80%) and toluene (5.33%) were the most abundant aromatics compounds, confirming the high potential of sludge as a feedstock for producing valuable chemical intermediates.