Developmental stuttering is a highly heritable, common speech condition characterized by prolongations, blocks and repetitions of speech. Although stuttering is highly heritable and enriched within families, the genetic architecture is largely understudied. We reasoned that there are both shared and distinct genetic variants impacting stuttering risk within sex and ancestry groups. To test this idea, we performed eight primary genome-wide association analyses of self-reported stuttering that were stratified by sex and ancestry, as well as secondary meta-analyses of more than one million individuals (99,776 cases and 1,023,243 controls), identifying 57 unique loci. We validated the genetic risk of self-reported stuttering in two independent datasets. We further show genetic similarity of stuttering with autism, depression and impaired musical rhythm across sexes, with follow-up analyses highlighting potentially causal relationships among these traits. Our findings provide well-powered insights into genetic factors underlying stuttering.