Lead-free novel n-type ternary nanohybrids were fabricated by blending separately synthesized, diamond like I–III–VI₂ and I–V–VI₂ (I-Cu, Ag, III-In, V-Sb, VI-Se) nanocrystals (NCs) in a multi-walled carbon nanotube (MWCNT) and polyaniline (PANI) matrix. A thermoelectric study of these nanohybrids was performed at room temperature in order to understand their utility as potential thermoelectric materials for advanced applications. Electrical conductivity, thermal conductivity and Seebeck coefficient were measured and the thermoelectric performance was evaluated at room temperature. All ternary nanohybrids revealed an n-type behavior with relatively higher electrical conductivity in the order of 10³ S m⁻¹. Among the CuInSe₂ (CIS), AgInSe₂ (AIS) and CuSbSe₂ (CSS)-based hybrids, chalcostilbite (i.e., CSS/MWCNT/PANI) showed a good performance at room temperature with a power factor of 1.16 μW m⁻¹ K⁻² and Seebeck coefficient of −23.5 μV K⁻¹. A possible mechanism of the charge transport for the ternary hybrid was also discussed. The present article highlights the potentiality of different lead-free ternary metal selenide NPs in hybrid forms for thermoelectric applications.