Abstract: We demonstrate all-optical linear polarization control in semiconductor microcavities using an exciton-polariton condensate in an elliptically shaped optical trap. The cavity inherent TE-TM splitting lifts the pseudospin degeneracy of the anisotropic trap ground state,the emerging fine structure modes are shown to be polarized linearly parallel and perpendicular to the trap major axis. We show stable polariton condensation into the excited pseudospin mode with high degree of linear polarization which rotates as we rotate the trap. Our findings show a new type of polarization control with exciting perspectives in both spinoptronics and studies on extended systems of interacting nonlinear optical elements with anisotropic coupling strength and adjustable fine structure.