  We predict nonlinear optical polarization rotation in two dimensional
massless Dirac systems including graphene and 8-$Pmmn$ borophene. When
illuminated, a continuous wave optical field leads to a nonlinear steady state
of photo-excited carriers in the medium. The photo-excited population inversion
and the inter-band coherence gives rise to a finite transverse optical
conductivity, $\sigma_{xy} (\omega)$. This in turn leads to definitive
signatures in associated Kerr and Faraday polarization rotation, which are
measurable in a realistic experimental scenario.
