Cyclin D1b is a splice variant of the cell cycle regulator Cyclin D1 and is known to harbor divergent and highly oncogenic functions in human disease. While Cyclin D1b is induced during disease progression in many cancer types, the mechanisms underlying Cyclin D1b function remain poorly understood. Herein, models of human disease were utilized to resolve the downstream pathways requisite for the pro-tumorigenic functions of Cyclin D1b. Specifically, it was shown that Cyclin D1b modulates the expression of a large transcriptional network that cooperates with AR signaling to enhance tumor cell growth and invasive potential. Notably, Cyclin D1b promoted AR-dependent activation of genes associated with metastatic phenotypes. Further exploration determined that transcriptional induction of SNAI2 (Slug) was essential for Cyclin D1b- mediated proliferative and invasive properties, implicating Slug as a critical driver of disease progression. Importantly, Cyclin D1b expression highly correlated with that of Slug in clinical samples of advanced disease. Further, in vivo analyses provided strong evidence that Slug enhances both tumor growth and homing to distal soft tissues. Collectively, these findings reveal the underpinning mechanisms behind the pro-tumorigenic functions of Cyclin D1b, and demonstrate that the convergence of the Cyclin D1b-AR and Slug pathways results in the activation of processes critical for the promotion of lethal tumor phenotypes.