  We study the imprints of high scale non-thermal leptogenesis on cosmic
microwave background (CMB) from the measurements of inflationary spectral index
($n_s$) and tensor-to-scalar ratio ($r$), which otherwise is inaccessible to
the conventional laboratory experiments. We argue that non-thermal production
of baryon (lepton) asymmetry from subsequent decays of inflaton to heavy
right-handed neutrinos (RHN) and RHN to SM leptons is sensitive to the
reheating dynamics in the early Universe after the end of inflation. Such
dependence provides detectable imprints on the $n_s-r$ plane which is well
constrained by the Planck experiment. We investigate two separate cases, (I)
inflaton decays to radiation dominantly and (II) inflaton decays to RHN
dominantly which further decays to the SM particles to reheat the Universe
adequately. Considering a class of $\alpha-$ attractor inflation models, we
obtain the allowed mass ranges for RHN for both cases and thereafter furnish
the estimates for $n_s$ and $r$. The prescription proposed here is general and
can be implemented in various kinds of single-field inflationary models given
the conditions for non-thermal leptogenesis are satisfied.
