  We study thermal and non-thermal resonant leptogenesis in a general setting
where a heavy scalar $\phi$ decays to right-handed neutrinos (RHNs) whose
further out-of-equilibrium decay generates the required lepton asymmetry.
Domination of the energy budget of the Universe by the $\phi$ or the RHNs
alters the evolution history of the primordial gravitational waves (PGW), of
inflationary origin, which re-enter the horizon after inflation, modifying the
spectral shape. The decays of $\phi$ and RHNs release entropy into the early
Universe while nearly degenerate RHNs facilitate low and intermediate scale
leptogenesis. We show that depending on the coupling $y_R$ of $\phi$ to
radiation species, RHNs can achieve thermal abundance before decaying, which
gives rise to thermal leptogenesis. A characteristic damping of the GW spectrum
resulting in two knee-like features or one knee-like feature would provide
evidence for low-scale thermal and non-thermal leptogenesis respectively. We
explore the parameter space for the lightest right-handed neutrino mass
$M_1\in[10^2,10^{14}]$ GeV and washout parameter $K$ that depends on the
light-heavy neutrino Yukawa couplings $\lambda$, in the weak ($K < 1$) and
strong ($K > 1$) washout regimes. The resulting novel features compatible with
observed baryon asymmetry are detectable by future experiments like LISA and
ET. By estimating signal-to-noise ratio (SNR) for upcoming GW experiments, we
investigate the effect of the scalar mass $M_\phi$ and reheating temperature
$T_\phi$, which depends on the $\phi-N$ Yukawa couplings $y_N$.
