The coal gangue (CG) is a noncombustible waste mechanically separated from coal during the sorting or coal washing phase of mining. Because of the negative implications of unscientific disposal of CG, there is a need to utilize it in bulk civil engineering works. More precisely, the application of CG in earthworks facilitates its bulk application. The present study aims to evaluate the unconfined compressive strength (UCS) characteristics of lime- and gypsum-treated CG. The lime and gypsum dosages were varied from 2 to 6 % and 0.5 to 1.5 %, respectively. The influence of lime and gypsum addition on the UCS was evaluated for varying curing periods (CPs) of 7, 14, and 28 days. An exponential model is developed to evaluate UCS based on the experimental data using lime content, gypsum content, and CP. Further, attempts were made to estimate the optimum amounts of lime and gypsum content for satisfactory UCS performance of stabilized CG using target reliability-based design optimization (TRBDO). Furthermore, carbon footprint analysis (CFA) was performed to quantify the environmental benefits attainable by applying CG as subbase material in the pavement. The results showed that the maximum dry density increased from 1.74 to 1.84 g/cc for 4 % lime addition. The UCS of CG linearly increased with an increase in lime dosage, gypsum dosage, and CP. The highest increment of 1,050 % was attained for 1.5 % gypsum and 6 % lime addition. The CFA results indicate that CG’s procurement (embodied) emissions are substantially higher, with an 88 % share in overall emissions. From the reliability studies, it is noted that the TRBDO is helpful in predicting the optimum dosages of lime and gypsum for the satisfactory performance of pavements. Copyright © 2021 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.