During mouse spinal cord development ventricular zone progenitor cells transition from producing neurons to producing glia at approximately embryonic day 11.5, a process known as the gliogenic switch. The transcription factors Nuclear factor I (NFI) A and B orchestrate this developmental transition, but the contribution of a third NFI member, NFIX, remains unknown. Here we reveal that NFIX is expressed by ventricular zone progenitor cells within the spinal cord after the onset of NFIA and NFIB expression, and after the gliogenic switch has occurred. Mice lacking NFIX exhibit normal neurogenesis within the spinal cord but aspects of terminal glial differentiation are impaired. Finally, we demonstrate that NFIA and NFIB can each transcriptionally activate NFIX expression. These data highlight the importance of the NFI family in regulating gliogenesis within the embryonic spinal cord, and reveal that NFIX is part of the downstream transcriptional program through which NFIA and NFIB promote gliogenesis in ventricular zone progenitor cells.