In this study, aerobic granular reactor (AGR) was used to treat landfill leachate by changing the concentrations of chemical oxygen demand (COD) (668 ± 110-1149 ± 93 mg/L), ammonia (NH₃–N) (30 ± 3.3-48 ± 1.3 mg/L), and phosphorus (PO₄–P) (147 ± 18-221 ± 17 mg/L). The average COD removal was gradually reduced from 81 to 75%, increasing COD concentrations from 668 ± 110 to 1149 ± 93 mg/L. In phase I, the maximum removal of COD (94%) and NH₃–N (85%) were observed at influent concentrations of 668 ± 110 mg/L and 30 ± 3.3 mg/L, respectively. Significant removal of PO₄–P was observed, resulting in a maximum of up to 87%, further reducing up to 34% due to an increase in influent PO₄–P concentration. The SVI₃₀ reduced from 77 mL/g to 24.15 mL/g towards the end of phase III indicates the formation of granular biomass. The stability of AGR was also investigated in extreme conditions like shut-down and shock-loading phases. The treatment of real leachate diluted with wastewater ($\sim$20:80% v/v) in AGR showed a significant COD, NH₃–N, and PO₄–P removal of 62%–65%, 61%–93%, and 56%–64%, respectively. Mass balance analysis indicated that the AGR requires a lower nitrogen percentage for microbial assimilation than the COD and phosphorus. Proteobacteria and Planctomycetes were identified as the predominant (80%) bacterial community in aerobic granules responsible for removing COD, NH₃–N, and PO₄–P from leachate using AGR. The maximum biodegradation rate ($r_{\max }$) and half-saturation constant ($K_{\mathrm{s}}$) of COD in AGR were determined as 123.5 mg/L h and 309 mg/L, respectively.