AbstractCircadian rhythms, as physiological systems with self‐regulatory functions in living organisms, are controlled by core clock genes and are involved in tumor development. The protein arginine methyltransferase 6 (PRMT6) serves as an oncogene in a myriad of solid tumors, including breast cancer. Hence, the primary aim of the current study is to investigate the molecular mechanisms by which the PRMT6 complex promotes breast cancer progression. The results show that PRMT6, poly(ADP‐ribose) polymerase 1 (PARP1), and the cullin 4 B (CUL4B)‐Ring E3 ligase (CRL4B) complex interact to form a transcription‐repressive complex that co‐occupies the core clock genePER3promoter. Moreover, genome‐wide analysis of PRMT6/PARP1/CUL4B targets identifies a cohort of genes that is principally involved in circadian rhythms. This transcriptional‐repression complex promotes the proliferation and metastasis of breast cancer by interfering with circadian rhythm oscillation. Meanwhile, the PARP1 inhibitor Olaparib enhances clock gene expression, thus, reducing breast carcinogenesis, indicating that PARP1 inhibitors have potential antitumor effects in high‐PRMT6 expression breast cancer.