Vinculin is a highly conserved protein involved in cell adhesion and mechanotransduction, and both gain and loss of its activity causes defective cell behaviour. Here, we examine how altering vinculin activity perturbs integrin function within the context of $Drosophila$ development. Whereas loss of vinculin produced relatively minor phenotypes, gain of vinculin activity, via a loss of head-tail autoinhibition, caused lethality. The minimal domain capable of inducing lethality is the talin-binding D1 domain, and this appears to require talin-binding activity, as lethality was suppressed by competition with single vinculin binding sites from talin. Activated $Drosophila$ vinculin triggered the formation of cytoplasmic adhesion complexes via the rod of talin, but independently of integrin. These complexes contain a subset of adhesion proteins but no longer link the membrane to actin. The negative effects of hyperactive vinculin were segregated into morphogenetic defects caused by the whole head domain, and lethality caused by the D1 domain. These findings demonstrate the critical importance of the tight control of vinculin's activity.