Galectin-1, a member of a family of highly conserved glycan-binding proteins, has emerged as a regulator of immune cell tolerance and homeostasis. This endogenous lectin widely expressed at sites of inflammation and tumour growth, has been postulated as an attractive immunosuppressive agent to restore immune cell tolerance and homeostasis in autoimmune and inflammatory settings. On the other hand, galectin-1 contributes to different steps of tumour progression including cell adhesion, migration and tumour-immune escape, suggesting that blockade of galectin-1 might result in therapeutic benefits in cancer. Recent findings implicating galectin-glycoprotein lattices as selective regulators of inflammatory responses have provided new insights into the understanding of the molecular bases of galectin-1-induced immunoregulation. Here the authors review the dual role of galectin-1 as a selective immunosuppressive agent in T helper (T(H))1 and T(H)17-mediated inflammatory/autoimmune disorders and a potential therapeutic target in cancer and metastasis.