Impaired musical rhythm abilities and developmental speech-language related disorders are biologically and clinically intertwined. Prior work examining their relationship has primarily used small samples; here, we studied associations at population-scale by conducting the largest systematic epidemiological investigation to date (total N = 39,092). Based on existing theoretical frameworks, we predicted that rhythm impairment would be a significant risk factor for speech-language disorders in the general adult population. Findings were consistent across multiple independent datasets and rhythm subskills (including beat synchronization and rhythm discrimination), and aggregate meta-analyzed data showed that rhythm impairment is a modest but consistent risk factor for developmental speech, language, and reading disorders (OR = 1.32 [1.14 – 1.49]; p < .0001). Further, cross-trait polygenic score analyses indicate shared genetic architecture between musical rhythm and reading abilities, providing evidence for genetic pleiotropy between rhythm and language-related phenotypes.