The generation of cortical projection neurons relies on the coordination of radial migration with branching. Here, we report that the multisubunit histone acetyltransferase Elongator complex, which contributes to transcript elongation, also regulates the maturation of projection neurons. Indeed, silencing of its scaffold (Elp1) or catalytic subunit (Elp3) cell-autonomously delays the migration and impairs the branching of projection neurons. Strikingly, neurons defective in Elongator show reduced levels of acetylated α-tubulin. Reduction of α-tubulin acetylation via expression of a nonacetylatable α-tubulin mutant leads to comparable defects in cortical neurons and suggests that α-tubulin is a target of Elp3. This is further supported by the demonstration that Elp3 promotes acetylation and counteracts HDAC6-mediated deacetylation of this substrate in vitro. Our results uncover α-tubulin as a target of the Elongator complex and suggest that a tight regulation of its acetylation underlies the maturation of cortical projection neurons.