We propose a self-interacting dark matter (DM) scenario with a right handed neutrino (RHN) portal to the standard model (SM). The dark sector consists of a particle DM, assumed to be a Dirac fermion, and a light mediator in terms of a dark Abelian vector boson to give rise the required velocity-dependent self-interactions in agreement with astrophysical observations. Irrespective of thermal or nonthermal production of such a DM, its final relic remains underabundant due to efficient annihilation rates of DM into light mediators by virtue of large self-interaction coupling. We then show that a feeble portal of DM-SM interaction via a RHN offers a possibility to fill the relic deficit of DM via the late decay of a RHN. As RHNs also arise naturally in seesaw models explaining the origin of light neutrino masses, we outline two UV-complete realizations of the minimal setup in terms of scotogenic and gauged B-L frameworks where connection to neutrino mass and other phenomenology like complementary discovery prospects are discussed. © 2022 authors. Published by the American Physical Society.