  We consider the $SU(6)$ GUT model as an explanation for the diphoton final
state excess, where the masses of all associated particles are linked with a
new symmetry breaking scale. In this model, the diphoton final states arise due
to loops involving three pairs of new vector-like particles having the same
quantum numbers as down-type quarks and lepton doublets. These new vector-like
fermions are embedded alongside the SM fermions into minimal anomaly-free
representations of the $SU(6)$ gauge symmetry. The $SU(6)$ symmetry is broken
to the Standard Model times $U(1)_X$ at the GUT scale, and masses for the
vector-like fermions arise at the TeV scale only after the residual $U(1)_X$
symmetry is broken. The vector-like fermions do not acquire masses via breaking
of the SM symmetry at the EW scale. The field which is responsible for the
newly observed resonance belongs to the $\bar{6}_H$ representation. The dark
matter arises from the SM singlet fermion residing in $\bar{6}$ and is of
Majorana type. We explicitly demonstrate gauge coupling unification in this
model, and also discuss the origin of neutrino masses. In addition to the
diphoton final states, we make distinctive predictions for other final states
which are likewise accessible to the ongoing LHC experimental effort.
