Transition metal atom (Co) substituted synthetic tetrahedrite compounds Cu$_{12-x}$Co$_x$Sb$_4$S$_{13}$ (x = 0, 0.5, 1.0, 1.5, 2.0) were prepared by solid state synthesis. X-Ray Diffraction (XRD) patterns revealed tetrahedrite as the main phase, whereas for the compounds with x = 0, 0.5 a trace of impurity phase Cu$_3$SbS$_4$ was observed. The surface morphology showed a large grain size with low porosity, which indicated appropriate compaction for the hot pressed samples. The phase purity, as monitored by Electron Probe Micro Analysis (EPMA) is in good agreement with the XRD data. The elemental composition for all the compounds almost matched with the nominal composition. The X-ray Photoelectron Spectroscopy (XPS) data showed that Cu existed in both +1 and +2 states, while Sb exhibited +3 oxidation states. Elastic modulus and hardness showed a systematic variation with increasing Co content. The electrical resistivity and Seebeck coefficient increased with increase in the doping content due to the decrease in the number of carriers caused by the substitution of Co$^{2+}$ on the Cu$^{1+}$ site. The positive Seebeck coefficient for all samples indicates that the dominant carriers are holes. A combined effect of resistivity and Seebeck coefficient leads to the maximum power factor of 1.76 mW m$^{-1}$K$^{-2}$ at 673 K for Cu$_{11.5}$Co$_{0.5}$Sb$_4$S$_{13}$. This could be due to the optimization in the carrier concentration by the partial substitution of Co$^{2+}$ on both the Cu$^{1+}$ as well as Cu$^{2+}$ site at the same doping levels, which is also supported by the XPS data. The total thermal conductivity systematically decreased with increase of doping content as it is mainly influenced by the decrease of carrier thermal conductivity. The maximum thermoelectric figure of merit zT = 0.98 was obtained at 673 K for Cu$_{11.5}$Co$_{0.5}$Sb$_4$S$_{13}$.