<p>Mung bean seed quality is greatly affected by the inherent difficulty of determining the optimal harvest time, which is further complicated by asynchronous flowering and pod maturation, resulting in considerable losses. This study assessed how harvesting maturity impacts seed quality of five mung bean varieties, namely Nduru, Nuru, TARI Green Gram 1 (TG1), TARI Green Gram 2 (TG2), and Imara, harvested at 60, 70, 80, and 90 days after sowing (DAS). A split-plot design under a randomized complete block design was used in the field, and a two-factor factorial arrangement was applied in the laboratory. Significant varietal differences (<i>p</i> ≤ 0.05) were observed for 1000-seed weight, seed geometric mean, seedling length, seedling dry weight, and seedling vigour index I and II, while germination percentage (<i>p</i> = 0.1) and the percentage of abnormal seedlings (<i>p</i> = 0.25) showed no significant effect. Harvesting maturity significantly influenced 1000-seed weight (<i>p</i> = 0.0003), seed count per 100&#xa0;g (<i>p</i> = 0.001), germination, percentage of abnormal seedlings, seedling dry weight, and vigour index II (<i>p</i> ≤ 0.05). The interaction between variety and maturity notably affected seedling dry weight and vigour indices, with TG1 and TG2 performing best at 90 DAS. Principal component analysis showed that the first two components explained over 60% and 80% of the variance for harvesting maturity and variety, respectively. Strong correlations were found between 1000-seed weight and vigour index II (<i>r</i> = 0.64), and between germination and vigour index I (<i>r</i> = 0.65). These findings emphasise the importance of choosing suitable varieties and harvesting at the right time to enhance mung bean seed quality and crop performance.</p>