Immunoglobulin heavy constant chain gamma 1 (IGHG1) is highly expressed in a variety of cancers and is considered an emerging prognostic marker. Overexpression of IGHG1 in breast cancer tissues has also been demonstrated, but an in-depth analysis of its role in disease progression has not been explored. In this study, we used a range of molecular and cell-based assays to show that increased expression of IGHG1 in breast cancer cells activates AKT and vascular endothelial growth factor (VEGF) signaling, leading to enhanced cell proliferation, invasion, and angiogenesis. We further showed that IGHG1-silencing can suppress the neoplastic characteristics of breast cancer cells in vitro and suppresses tumor growth in nude mice. These data reveal a key role of IGHG1 in the malignant progression of breast cancer cells and highlight its potential as a prognostic marker and therapeutic target to control metastasis and angiogenesis in malignant breast tissue.