Because of the ever-increasing consumption of energy, higher-efficiency thermoelectric materials are in more demand. In this regard, initially, Zn x Ni (1−x) Fe 2 O 4 nanoparticles were synthesized using a co-precipitation technique and investigated using Rietveld refinement and Brunauer−Emmett−Teller (BET) analyses. Then, they were dispersed in water to obtain stable 1 vol % of aqueous Zn x Ni (1−x) Fe 2 O 4 nanofluids and their viscous, electrical, thermal, and thermoelectric properties were analyzed in the absence and presence of a magnetic field. The Rietveld refinement revealed the formation of single phase spinel ferrite structures and cationic distribution of Zn x Ni (1−x) Fe 2 O 4 nanoparticles, whereas BET analysis revealed the surface area of the nanoparticles. The viscosity studies proved the pseudo-plastic shear thinning behavior and dipole−dipole interactions of Zn x Ni (1−x) Fe 2 O 4 nanofluids. The electrical conductivity, thermal conductivity, and Seebeck coefficient studies revealed that the maximum enhancement was observed for the Zn 0.2 Ni 0.8 Fe 2 O 4 nanofluid, which was attributed to the enhanced electrical double layer formation and Brownian motion of nanoparticles in the nanofluid. The enhancement in the properties of synthesized nanofluids in the presence of a magnetic field was attributed to the formation of chain-like structures, which was substantiated through the magneto-viscosity studies. The thermoelectric energy conversion efficiency of Zn x Ni (1−x) Fe 2 O 4 nanofluids was calculated which showed that the maximum enhancement of 27% was observed in the Zn 0.2 Ni 0.8 Fe 2 O 4 nanofluid at 770 G. The observed results proved that the synthesized nanofluids are magnetically tunable thermoelectric materials which are suitable for waste heat energy harvesting applications.