Enteropathogenic and enterohemorrhagic E. coli (EPEC and EHEC) are extracellular pathogens that reorganize the host cell cytoskeleton to form "actin pedestals" beneath the tightly adherent bacteria, a critical step in pathogenesis. EPEC and EHEC inject effector proteins that manipulate host cell signalling cascades to trigger pedestal assembly. One such effector, EspG, has been reported to bind and activate p21-activated kinase (PAK), a key cytoskeletal regulator, but the function of this interaction, and whether it impacts on pedestal assembly are unknown. Here, we demonstrate that deletion of espG significantly impairs pedestal formation and attachment by both EPEC and EHEC. This role of EspG is shown to be dependent on its interaction with PAK. Unexpectedly EspG was only able to subvert PAK in the presence of Rho family small GTPases, which function to both concentrate PAK at the membrane and stimulate PAK activation. Our findings reveal a novel mechanism by which EspG hijacks PAK and sustains its active state to drive bacterial attachment to host cells.