Abstract: The accumulation of coal gangue, a major solid waste generated from coal mining activities, poses increasingly severe environmental and ecological risks, such as soil contamination, water pollution, and landscape destruction. As an advanced thermal conversion technology, pyrolysis has emerged as a promising approach for coal gangue resource utilization due to its advantages of clean disposal, high efficiency, and minimal secondary pollution. Among various pyrolysis strategies, the co-pyrolysis of industrial organic sewage sludge with coal gangue has been considered an effective approach to enhance the pyrolysis characteristics of coal gangue and to achieve synergistic resource utilization of the solid wastes. In this study, coupled thermogravimetry-mass spectrometry (TG-MS) and Fourier transform infrared spectroscopy (FTIR) techniques were employed to investigate the thermal decomposition characteristics, kinetic properties, volatile distribution, and interactions during the co-pyrolysis of coal gangue and sludge, enabling real-time monitoring and comprehensive analysis of the pyrolysis process. The results revealed a significant synergistic effect in the co-pyrolysis of the mixtures. Specifically, the main pyrolysis process of the mixtures consisted of two distinct stages: the first stage (210–410 °C) dominated by the decomposition of light organic components in sludge; and the second stage (410–584 °C), primarily involving the cracking of heavy organic matter in both coal gangue and sludge. Notably, the differences between the experimental and theoretical thermogravimetric (TG) curves of the mixtures were negative, serving as direct evidence of the synergistic effect. Furthermore, calculations of key pyrolysis performance parameters confirmed that the addition of sludge effectively improved the overall pyrolysis performance of the mixtures. Three widely used pyrolysis kinetic models—Kissinger–Akahira–Sunose, Ozawa–Flynn–Wall, and Starink—were applied to calculate the activation energy. The results showed that the activation energies of coal gangue and sludge alone ranged from 314.00 to 321.55 kJ/mol and 236.13 to 240.73 kJ/mol, respectively. A direct comparison of the data indicated that the addition of sludge significantly reduced the activation energy required for the co-pyrolysis of the mixtures, thereby lowering the energy barrier for thermal decomposition. Additionally, FTIR and MS results demonstrated that while coal gangue produced almost no detectable volatile products due to its high ash content, the interactions between metal minerals in coal gangue and volatile components released from sludge significantly promoted the generation of light hydrocarbon species (e.g., \mathrmC_2 \mathrmH_2^+ , \mathrmC_3 \mathrmH_5^+ , and \mathrmC_3 \mathrmH_7^+ frgments). In conclusion, this study demonstrates that the synergistic effect in the co-pyrolysis of coal gangue and industrial organic sewage sludge enhances pyrolysis performance, reduces the activation energy, and increases the yield of high-value gaseous products, providing a valuable theoretical reference and technical support for the resource utilization of coal gangue via pyrolysis and offering a sustainable solution for the joint disposal of coal gangue and sludge.