  We propose a novel scenario of generating lepton asymmetry via annihilation
and coannihilation of dark sector particles including t-channel processes. In
order to realistically implement this idea, we consider the scotogenic model
having three right handed neutrinos and a new scalar doublet, all of which are
odd under an in-built $Z_2$ symmetry. The lightest $Z_2$ odd particle, if
electromagnetically neutral, can be a dark matter candidate while annihilation
and coannihilation between different $Z_2$ odd particles into standard model
leptons serve as the source of lepton asymmetry. The light neutrino masses
arise at one loop level with $Z_2$ odd fields going inside the loop. We show
that experimental data related to light neutrinos, dark matter relic abundance
and baryon asymmetry can be simultaneously satisfied in the model for two
different cases: one with fermion dark matter and the other with scalar dark
matter. In both scenarios, t-channel annihilation as well as coannihilation of
$Z_2$ odd particles play a non-trivial role in producing the non-zero CP
asymmetry. Both the scenarios remain allowed from DM direct detection while
keeping the scale of leptogenesis as low as TeV or less, lower than the one for
vanilla leptogenesis scenario in scotogenic model along with the additional
advantage of explaining the baryon-dark matter coincidence to some extent. Due
to such low scale, the model is testable through rare decay experiments looking
for charged lepton flavour violation.
