In this study, the development of a new white beech mushroom (Hypsizygus marmoreus) cultivar, ‘Baekmaru24’, is described, and its growth characteristics and field adaptability are evaluated. ‘Baekmaru24’ was bred from the parent strains, KMCC05528 and KMCC05529, through controlled crossing and multi-stage line selection, resulting in the final elite line, ‘HWD-22-116’. Mycelial growth tests demonstrated that the cultivar had superior growth under low temperatures (10–15 °C) and on YM medium, with optimal growth at 20–25 °C. In indoor bottle cultivation, the per-bottle yield was 146 g per 850 mL, which was 8% higher than that of the control cultivar (135 g). The fruiting bodies had stipes with a mean of 70.5 mm, which is approximately 10 mm longer than that of the control, and they had highly uniform clusters, enhancing marketability. Field trials at two farms confirmed a significant increase in yield of approximately 11 % over existing commercial cultivars, together with a generally superior morphology, including larger caps, longer stipes, and greater tissue firmness. Somatic incompatibility testing revealed a distinct demarcation zone between ‘Baekmaru24’ and its parent strains, indicating that it is a genetically independent cultivar. Overall, these results demonstrate that ‘Baekmaru24’ has stable growth, high productivity, and favorable fruiting-body characteristics under both controlled and farm conditions, supporting its potential as a high-quality commercial mushroom cultivar.