Quaternary copper-based thermoelectric materials are emerging as practicable alternatives for the current efficient thermoelectric materials. The solvothermal method synthesizes the samples of Cu2-xCoxNiSnS4 (0 ≤ x ≤ 0.1). XRD results showed that Co-doped Cu2NiSnS4 exhibits a cubic crystal structure having a space group of F-43m. The energy bandgap was seen to be decreasing from the range of 1.52 eV–1.39 eV with Co-doping. HR-SEM analysis reveals the garland-like flower structure of Co-doped Cu2NiSnS4, which was formed by the arrangement of nanosheets. The Seebeck coefficient increases with increasing Co content. However, the sample with x = 0.075 cobalt doped (CC-4) showed a high Seebeck coefficient of 255 μV/K and increased electrical conductivity of 5.94 × 103 S/m at 573 K. Hence, the power factor has seen reaching a high value of 230 μW/mK at 573 K. The Hall effect measurements showed the samples’ p-type nature and a increment in hole concentration, 1019 to 1020 cm-3. The increased phonon scattering at the nanosheets and grains reduced its thermal conductivity, showing a minimum value of 0.46 W/mK at 573 K for the CC-4 sample. With an enhanced power factor value and minimal thermal conductivity, a high figure of merit (zT) value of 0.282 was attained at 573 K for the CC-4 sample. The work offers a great resource for creating high-performance, nontoxic thermoelectric materials using Cu2-xCoxNiSnS4 (0 ≤ x ≤ 0.1).