  Optical anisotropy is usually treated as an unfavorable condition for the
magneto-optical measurements since it is known to diminish the Faraday rotation
concerning the case of the isotropic medium. Here we show that the situation
could be quite opposite: a phenomenon of birefringence mediated enhancement of
the magneto-optical activity appears if the incident light polarization and
angle of incidence are set properly. The present study relies on the
experimental, analytical, and numerical studies of iron borate
$\mathrm{FeBO_3}$ crystals. We demonstrate a significant increase of the
magneto-optical activity resulting in nearly $100\%$ magneto-optical light
modulation magnitude. The approach applies to other types of birefringent
crystals with the magneto-optical response that makes it crucial for various
practical applications, including magneto-optical microscopy, pump-probe
studies, and others.
