Cancer-associated fibroblasts (CAF) generate an extracellular matrix (ECM) which provides a repository for factors that promote pancreatic cancer progression. Here, we establish that CAF contribution to pancreatic tumor initiation, i.e. stemness, depends on fibronectin (FN) as a scaffold required for assembly of a collagen-containing fibrotic ECM with a critical dependence on the FN-binding integrins, α5β1 and αvβ3. CAF matrix assembly can be prevented by knockdown of FN, ITGA5, or ITGB3, or by a bispecific antibody with dual recognition of α5β1 and αvβ3 that can also destabilize a pre-existing matrix. In mice, the ability of CAFs to produce a stiff collagenous matrix and accelerate tumor initiation can be blocked by knockdown of FN or FN-binding integrins, or systemic treatment with the α5β1/αvβ3 bispecific antibody. Together, these results reveal that dual targeting of the FN-binding integrins α5β1/αvβ3 can block the ability of CAFs and their matrix from enhancing pancreatic cancer stemness and progression.