The response of polyelectrolytes to specific environmental conditions has attracted materials scientists for decades. Recently, end-grafted polyelectrolytes, denoted “polyelectrolyte brushes”, have flourished due to their relevance in biological systems and in various applications in materials science and nanotechnology. We combined the surface forces apparatus (SFA), atomic force microscopy (AFM) techniques, and coarse-grained molecular dynamics (MD) simulation method to study the structure of high-density polystyrene sulfonate (PSS) brushes in a variety of solvent conditions. Surface force and AFM measurements show that the presence of multivalent counterions, even at relatively low concentrations, can strongly affect the structure of polyelectrolyte brushes.Taken together, AFM, SFA, and MD in unison described a system in which solvophobic and multivalent ion induced effects together drive strong phase separation, with electrostatic bridging of polyelectrolyte chains playing an essential role in the collapsed structure formation. The subtle details of a polyelectrolyte brush’s environment can strongly dictate its structural features and potential applications.