  We propose a non-supersymmetric $\mathrm{E}_{6}$ GUT with the scalar sector
consisting of $\mathbf{650}\oplus \mathbf{351'} \oplus \mathbf{27}$. Making use
of the first representation for the initial symmetry breaking to an
intermediate stage, and the latter two representations for second-stage
breaking to the Standard Model and a realistic Yukawa sector, this theory
represents the minimal $\mathrm{E}_{6}$ GUT that proceeds through one of the
intermediate stages that are novel compared to $\mathrm{SU(5)}$ or
$\mathrm{SO}(10)$ GUT: trinification $\mathrm{SU}(3)_C\times
\mathrm{SU}(3)_L\times \mathrm{SU}(3)_R$, $\mathrm{SU}(6)\times \mathrm{SU}(2)$
and flipped $\mathrm{SO}(10)\times\mathrm{U}(1)$. We analyze these
possibilities under the choice of vacuum that preserves a $\mathbb{Z}_{2}$
``spinorial parity'', which disentangles the chiral and vector-like fermions of
$\mathrm{E}_{6}$ and provides a dark matter candidate in the form of a (scalar)
inert doublet. Three cases are shown to consistently unify under the extended
survival hypothesis (with minimal fine-tuning): trinification symmetry
$\mathrm{SU}(3)_C\times \mathrm{SU}(3)_L\times \mathrm{SU}(3)_R$ with either
$LR$ or $CR$ parity, and $\mathrm{SU}(6)_{CR}\times\mathrm{SU}(2)_L$. Although
the successful cases give a large range for proton lifetime estimates, all of
them include regions consistent with current experimental bounds and within
reach of forthcoming experiments. The scenario investigated in this paper
essentially represents the unique (potentially) viable choice in the class of
$\mathrm{E}_{6}$ GUTs proceeding through a novel-symmetry intermediate stage,
since non-minimal alternatives seem to be intrinsically non-perturbative.
