Soybean (Glycine max) is the most important dicot crop worldwide, and is increasingly used as a model legume due to the wide availability of genomic soybean resources; however, the slow generation times of soybean plants are currently a major hindrance to research. Here, we demonstrate a method for accelerating soybean breeding in compact growth chambers, which greatly shortens the generation time of the plants and accelerates breeding and research projects. Our breeding method utilizes commonly used fluorescent lamps (220 µmol m-2 s-1 at the canopy level), a 14-h light (30 °C)/10-h dark (25 °C) cycle, and carbon dioxide (CO2) supplementation over 400 ppm. Using this approach, the generation time of the best-characterized elite Japanese soybean cultivar, Enrei, was shortened from 102-132 reported in the field to just 70 days, thereby allowing up to 5 generations per year instead of the 1-2 generations currently possible in the field and/or greenhouse. The method also facilitates the highly efficient and controlled crossing of soybean plants. Our method uses CO2 supplementation to promote the growth and yield of plants, appropriate light and temperature conditions to reduce the days to flowering, and the reaping and sowing of immature seeds to greatly shorten the reproductive period. Thus, the appropriate parameters enable to accelerate soybean breeding in the compact growth chambers commonly used for laboratory research. The parameters used in our method could therefore be optimized for other species, cultivars, accessions, and experimental designs to facilitate rapid breeding in a wide range of crops.