Advanced gastric cancer (GC) poses a significant threat to public health, leading to substantial consumption of healthcare resources due to its aggressive nature and poor prognosis. Hairy and enhancer of split 6 (Hes6), a member of the mammalian homologs of Drosophila’s hairy and enhancer of split (HES) family, functions as a transcriptional cofactor owing to its unique structural features. Previous studies have indicated that Hes6 expression is elevated in several malignant tumors, contributing to the enhanced proliferation and invasion of tumor cells. However, the precise role and underlying mechanisms of Hes6 in gastric cancer initiation and progression remain poorly understood. In this study, we demonstrate that Hes6 expression is significantly up-regulated in gastric cancer tissues, with elevated levels of Hes6 correlating with poor prognosis in certain patient cohorts. Functionally, Hes6 mediates gastric cancer cells to obtain stronger proliferation, migration, and invasion abilities by activating the PI3K/AKT signaling pathway, thereby accelerating tumor progression. Moreover, Hes6 interacts with the Twist1 protein, stabilizing it and facilitating the epithelial-mesenchymal transition (EMT). Collectively, these findings offer valuable insights into the regulatory mechanisms underlying gastric cancer progression, highlighting the potential of transcriptional cofactors, such as Hes6, in PI3K/AKT signaling as promising targets for therapeutic intervention in gastric cancer.