Human brain evolution is associated with expansion and folding of the neocortex. Increased diversity in neural progenitor (NP) populations (such as basally located radial glia [RG], which reside in an enlarged outer subventricular zone [OSVZ]) likely contributes to this evolutionary expansion, although their characteristics and relative contributions are only partially understood. Through single-cell transcriptional profiling of sorted human NP subpopulations, we identified the primate-specific TMEM14B gene as a marker of basal RG. Expression of TMEM14B in embryonic NPs induces cortical thickening and gyrification in postnatal mice. This is accompanied by SVZ expansion, the appearance of outer RG-like cells, and the proliferation of multiple NP subsets, with proportional increases in all cortical layers and normal lamination. TMEM14B drives NP proliferation by increasing the phosphorylation and nuclear translocation of IQGAP1, which in turn promotes G1/S cell cycle transitions. These data show that a single primate-specific gene can drive neurodevelopmental changes that contribute to brain evolution.