A typical sorghum spikelet produces a single fertile floret, resulting in a single‐grain spikelet morphology. However, the multiple-grain spikelet (MGS) sorghum germplasm, contains more than half of the double-grain spikelets per panicle and exhibits an unusual spikelet architecture in which two mature grains are produced within a single spikelet. Despite this, the genetic basis underlying this trait has remained unclear. Through extensive genetic analysis, we have identified a single recessive gene, MGS1, which encodes a MIKC type MADS-box transcription factor responsible for the MGS trait. Two natural variations, mgs19E and mgs1BA45, induced MGS by producing adjacent double-pistil primordia, resulting in a dramatic increase in grain number per panicle. This study illustrates an effective approach to enhancing grain number by utilizing the excellent mgs1 in future high-yield sorghum breeding designs.