Significance Pancreatic ductal adenocarcinoma (PDA) is the third leading of cause of cancer death in the United States and is predicted to be the second one by 2030. The tumor microenvironment is a major source of soluble mediators that influence tumor progression and hinder the success of therapeutic strategies. Using a genetically engineered mouse model and human cell-based systems, we identify galectin-1 (Gal1) as a critical soluble factor capable of regulating tumor–stroma crosstalk promoting proliferation, angiogenesis, and modulation of inflammatory responses, resulting in enhanced tumor development and metastasis. Our data provide an integrated view of the role of Gal1 in the PDA microenvironment and reinforce the high therapeutic value of Gal1 inhibition in PDA treatment.