  We propose a $B-L$ gauged extension of the Standard Model where light
neutrino masses arise from type III seesaw mechanism. Unlike the minimal $B-L$
model with three right handed neutrinos having unit lepton number each, the
model with three fermion triplets is however not anomaly free. We show that the
leftover triangle anomalies can be cancelled by two neutral Dirac fermions
having fractional $B-L$ charges, both of which are naturally stable by virtue
of a remnant $\mathbb{Z}_2 \times \mathbb{Z}'_2$ symmetry, naturally leading to
a two component dark matter scenario without any ad-hoc symmetries. We
constrain the model from all relevant phenomenological constraints including
dark matter properties. Light neutrino mass and collider prospects are also
discussed briefly. Due to additional neutral gauge bosons, the fermion triplets
in type III seesaw can have enhanced production cross section in collider
experiment.
