The decision to commit to the cell cycle is made during G1 through the concerted action of various cyclin-CDK complexes. Not only DNA replication, but also centriole duplication is initiated as cells enter the S-phase. The NIMA-related kinase NEK7 is one of many factors required for proper centriole duplication, as well as for timely cell cycle progression. However, its specific roles in these events are poorly understood. In this study, we find that depletion of NEK7 inhibits progression through the G1 phase in human U2OS cells via down-regulation of various cyclins and CDKs and also inhibits the earliest stages of procentriole formation. Depletion of NEK7 also induces formation of primary cilia in human RPE1 cells, suggesting that NEK7 acts at least before the restriction point during G1. G1-arrested cells in the absence of NEK7 exhibit abnormal accumulation of the APC/C cofactor Cdh1 at the vicinity of centrioles. Furthermore, the ubiquitin ligase APC/CCdh1 continuously degrades the centriolar protein STIL in these cells, thus inhibiting centriole assembly. Collectively our results demonstrate that NEK7 is involved in the timely regulation of G1 progression, S-phase entry, and procentriole formation.