MTHFD2 is highly overexpressed in breast cancer tissues, indicating that it might be used as a target in breast cancer treatment. This study aims to determine the role of MTHFD2 in breast cancer cell proliferation and the molecular pathways involved. In order to investigate MTHFD2 gene expression and its downstream pathways in breast cancer, we started our inquiry with a bioinformatics analysis. We then engineered breast cancer cell lines with either silenced or overexpressed MTHFD2 to study its effects on the cell cycle, proliferation, and the m6A methylation status of the gene IFRD1, predicted as a downstream target. Overexpression of MTHFD2 enhanced cellular proliferation, increased the proportion of EdU-positive cells, and accelerated progression into the S+G2/M phase. In contrast, MTHFD2 knockdown led to opposite effects. MTHFD2 and IFRD1 expression levels showed a strong positive association. Increased MTHFD2 activity boosted HDAC3 and mTOR phosphorylation, activating p70 S6K and 4EBP1-key regulators of cell proliferation. Moreover, overexpression of MTHFD2 was associated with reduced p53 acetylation and total protein levels. Silencing MTHFD2 decreased m6A methylation of IFRD1 RNA, whereas its overexpression increased methylation. Notably, IFRD1 siRNA transfection reversed the proliferative effects induced by MTHFD2 overexpression. Furthermore, MTHFD2 knockdown enhanced the sensitivity of breast cancer cells to several chemotherapeutic agents. In conclusion, MTHFD2 influences breast cancer cell proliferation by modulating the m6A methylation of IFRD1 RNA, which regulates the HDAC3/p53/mTOR pathway. These findings suggest that MTHFD2 inhibitors may synergistically enhance the efficacy of existing chemotherapies.