In epithelia, E-cadherin cytoplasmic tail is under cytoskeleton-generated tension via a link that contains β-catenin. A cotranscription factor, β-catenin, is also active in morphogenetic processes associated with epithelial-to-mesenchymal transition. β-Catenin signaling appears mechanically inducible and was proposed to follow phosphorylation-induced β-catenin release from E-cadherin. Evidence for this mechanism is lacking, and whether E-cadherin tension is involved is unknown. To test this, we combined quantitative fluorescence microscopies with genetic and pharmacological perturbations of epithelial-to-mesenchymal transition–induced cells in culture. We showed that β-catenin nuclear activity follows a substantial release from the membrane specific to migrating cells and requires multicellular deconfinement and Src activity. Selective nuclear translocation occurs downstream of focal adhesion kinase activation, which targets E-cadherin tension relaxation through actomyosin remodeling. In contrast, phosphorylations of the cadherin/catenin complex are not substantially required. These data demonstrate that E-cadherin acts as a sensor of intracellular mechanics in a crosstalk with cell-substrate adhesions that target β-catenin signaling.