Cancer cell adhesion to the vascular endothelium is a critical step of tumour metastasis. Endothelial surface molecule Thy-1 (CD90) is implicated in the metastatic process through its interactions with integrins and syndecans. However, how Thy-1 supports cell-cell adhesion in a dynamic mechanical environment is not known. Here we show that Thy-1 supports β1 integrin- and syndecan-4 (Syn4)-mediated contractility-dependent mechanosignalling of melanoma cells. At the single-molecule level, Thy-1 is capable of independently binding α5β1 integrin and syndecan-4 (Syn4) receptors. However, in the presence of both α5β1 and Syn4, the two receptors bind cooperatively to Thy-1, to form a trimolecular complex. This trimolecular complex displays a unique phenomenon we coin 'dynamic catch', characterized by abrupt bond stiffening followed by the formation of catch bonds, where force prolongs the bond lifetime. Thus, we reveal a new class of trimolecular interactions where force strengthens the synergistic binding of two co-receptors and modulates downstream mechanosignalling.