Ex vivo expansion of satellite cells and directed differentiation of pluripotent cells to mature skeletal muscle have proved difficult challenges for regenerative biology. Using a zebrafish embryo culture system with reporters of early and late skeletal muscle differentiation, we examined the influence of 2,400 chemicals on myogenesis and identified six that expanded muscle progenitors, including three GSK3β inhibitors, two calpain inhibitors, and one adenylyl cyclase activator, forskolin. Forskolin also enhanced proliferation of mouse satellite cells in culture and maintained their ability to engraft muscle in vivo. A combination of bFGF, forskolin, and the GSK3β inhibitor BIO induced skeletal muscle differentiation in human induced pluripotent stem cells (iPSCs) and produced engraftable myogenic progenitors that contributed to muscle repair in vivo. In summary, these studies reveal functionally conserved pathways regulating myogenesis across species and identify chemical compounds that expand mouse satellite cells and differentiate human iPSCs into engraftable muscle. Display omitted •Zebrafish blastomere culture system discovers six chemicals that promote myogenesis•Forskolin, an adenylyl cyclase activator, promotes mouse satellite cell expansion•A three-factor combination induces muscle differentiation of human iPSCs•Functionally conserved pathways regulate myogenesis across species This study uses a zebrafish embryo culture system to identify a set of small molecules that can expand postnatal muscle stem cells from mice and specify skeletal muscle differentiation from human induced pluripotent stem cells.