Zinc finger proteins (ZNFs) are the largest family of transcription factors, yet how they activate gene expression remains unclear. In this study, we identified Zincore, a protein complex consisting of QRICH1 and SEPHS1, as a ZNF-specific coregulator essential for embryonic development in mice and associated with developmental syndromes in humans. We also identified ZFP91 as a representative Zincore client, binding the conserved promoter motif CTTTAAR. Cryo-electron microscopy of a Zincore-ZFP91-DNA complex revealed a SEPHS1 arginine clamp to recognize the DNA-bound zinc finger domains. This mode of binding explains recognition of different ZNFs and stabilizes ZFP91 onto its cognate DNA motif. Thus, our study identified Zincore as a ZNF-specific coregulator essential for development, involving a distinctive mechanism that locks ZNFs onto DNA and regulates transcription.