In order to investigate the biological roles of CARM1 in breast cancer, we constructed MDA-MB-231 breast cancer cell line overexpressing CARM1 via tetracycline induction in this study. Western blot and RT-PCR were employed to determine the significant parameters. We revealed that the levels of both CARM1 protein and mRNA significantly increased after successful induction of CARM1 expression. In addition, the effects of overexpression of CARM1 on cell migration, proliferation, clonal formation and cell cycle were analyzed by cell scratch assay, plate cloning assay, cell proliferation assay, and flow cytometry. The results exhibited that the overexpression of CARM1 enhanced cell migration ability, clonal formation ability and cell proliferation ability of MDA-MB-231 cells. Moreover, the proportion of cells at S and G2/M phases were elevated in CARM1-overexpressed samples detected by flow cytometry analysis, implicating that the overexpression of CARM1 promoted the cell cycle process. In conclusion, this study suggested that the overexpression of CARM1 could promote the proliferation of cells, improve the ability of colony formation and migration, and accelerate the cell cycle process in MDA-MB-231 cells, which can serve as a foundation for further studies on CARM1 in breast cancer cells.