  MnSiN$_2$ is a transition metal nitride with Mn and Si ions displaying an
ordered distribution on the cation sites of a distorted wurtzite-derived
structure. The Mn$^{2+}$ ions reside on a 3D diamond-like covalent network with
strong superexchange pathways. We simulate its electronic structure and find
that the N anions in MnSiN$_2$ act as $\sigma$- and $\pi$-donors, which serve
to enhance the N-mediated superexchange, leading to the high N\'{e}el ordering
temperature of $T_N$ = 443 K. Polycrystalline samples of MnSiN$_2$ were
prepared to reexamine the magnetic structure and resolve previously reported
discrepancies. An additional magnetic canting transition is observed at
$T_\mathrm{cant}$ = 433 K and the precise canted ground state magnetic
structure has been resolved using a combination of DFT calculations and powder
neutron diffraction. The calculations favor a $G$-type antiferromagnetic spin
order with lowering to $Pc^\prime$. Irreducible representation analysis of the
magnetic Bragg peaks supports the lowering of the magnetic symmetry. The
computed model includes a 10$^\circ$ rotation of the magnetic spins away from
the crystallographic $c$-axis consistent with measured powder neutron
diffraction data modeling and a small canting of 0.6$^\circ$.
