Updated project metadata. CIC encodes a transcriptional repressor inactivated by loss-of-function mutations in several cancer types, indicating that it may function as a tumor suppressor. Recent data indicate that CIC may regulate cell cycle genes in humans; however, a thorough investigation of this proposed role has not yet been reported. Here, we used single-cell RNA sequencing technology to provide evidence that inactivation of CIC in human cell lines resulted in transcriptional dysregulation of genes involved in cell cycle control. We also mapped CIC’s protein-protein and genetic interaction networks, identifying interactions between CIC and members of the Switch/Sucrose Non-Fermenting (SWI/SNF) complex, as well as novel candidate interactions between CIC and cell cycle regulators. We further showed that CIC loss was associated with an increased frequency of mitotic defects in human cell lines and a mouse model. Overall, our study positions CIC as a cell cycle regulator and indicates that CIC loss can lead to mitotic errors, consistent with CIC’s emerging role as a tumor suppressor of relevance in several cancer contexts.