Legume crops, such as common bean (Phaseolus vulgaris L.), are significant in many Sub-Saharan African (SSA) countries including Eswatini, due to their numerous health benefits, high protein, fiber, vitamins, and minerals. Common beans are a staple food in many parts of the world and play a crucial role in nitrogen fixation, thereby improving soil fertility. However, climate change poses a significant threat to global food security and agricultural productivity. Eswatini's production declined due to drought, resulting in 700 metric tons in 2016 and 582.5 metric tons in 2023, falling far short of its 7,370 metric ton annual consumption, causing a supply deficit. The declines in common bean production compelled the country to rely on imports to meet local demand. The aim of this study was to assess the symbiotic performance and carbon accumulation of 27 common bean genotypes grown under field conditions. The experiment was conducted during the 2023/2024 cropping season. A Randomized Complete Block Design was used to test 27 common bean germplasms (11 red speckled sugar and 16 red mottled). The beans were planted in 13.5 m² plots (4.5 m × 3.0 m) with 50 cm inter-row and 10 cm intra-row spacings. Each plot consisted of 4 rows, with 20 plants per row. The data revealed significant differences among genotypes, with Cim-Rm-36 exceling in growth with 47.43 g.plant^-1 shoot dry matter yield and 1927.07 mg.plant^-1 carbon content, and Mwctz20a-Rm19 showing strong nitrogen fixation with 155.73 kg.ha^-1 of N-fixed. Genotype Mwctz20a-Rm-4 had the highest grain yield (1747.39 kg.ha^-1), showing high productivity potential, while Cim-Rm-14-Als61 had the highest nitrogen concentration (3.50%), indicating efficient nitrogen uptake. The δ13C values (-27.38‰ to -28.06‰) suggested similar water use efficiency among genotypes. The finding showed that common bean can make a significant contribution to N fertility, with carbon accumulation highlighting the potential for selecting genotypes with desirable traits to enhance crop productivity.