Over 200 years ago, large orchards of Acacia catechuAcacia catechu (L.f.) Willd., known as Khair, were established in the northwest regions of the country. However, these orchards are rapidly declining due to the introduction of exotic, fast-growing tree species. A. catechu is valuable for its hardwood, from which tannic acid is extracted for the dyeing industry, Ayurvedic medicine, and as a flavouring for Paan (Piper betle L.). Khair plant is also prized for its timber and used as a fuel source. This study assessed biomass and carbon storage capacity in a 20-year-old planted area using random sampling and a non-destructive plot selection method. The total height was 8.26 m, and the mean diameter at breast height was 21.60 cm, with annual growth rates of 1.08 cm and 0.41 m year−1. Biomass showed a strong positive correlation with diameter (r = 0.93) and total height (r = 0.75). The above-ground biomass was 19.15 kg tree−1 year−1, while that of the belowground was 3.83 kg tree−1 year−1, and the total biomass was 22.98 kg tree−1 year−1. A. catechu sequestered 6.89 t C ha−1, with a yearly carbon sequestrationCarbon sequestration rate of 0.35 t C ha−1. Although A. catechu exhibits comparatively slow growth, its indigenousIndigenous status, ecological resilience, drought tolerance, and socioeconomic significance, along with its capacity to sustain native biodiversity, make it a suitable candidate for reforestation and plantation initiatives in Bangladesh.