The thermoelectric skutterudite Ba0.3Co4Sb12 is a promising candidate for waste heat recovery applications. Recently, it was demonstrated that the addition of silver nanoparticles (Ag-NP) to Ba0.3Co4Sb12 increases both the thermoelectric figure of merit and electrical conductivity. This study is the first to examine the effect of Ag-NP addition on the material's mechanical properties. This study also found that the Young's modulus, E, shear modulus, G, and bulk modulus, B, decreased linearly with increasing volume fraction porosity, P. Resonant ultrasound spectroscopy was employed to measure the elastic moduli, and Vickers indentation was used to determine the hardness, H, and fracture toughness, K (C). Trends in the mechanical properties as a function of grain size, porosity, and the Ag-NP are discussed in terms of the pertinent literature. While K (C) was independent of Ag-NP addition, porosity, and grain size, both E and H decreased linearly with increasing porosity. In addition, this study is the first to identify (i) the Ag3Sb phase formed and (ii) the enhanced densification that occurs when the Ag-NP is sintered with Ba0.3Co4Sb12 powders, where both effects are consistent with the eutectic and peritectic reactions observed in the binary phase diagram Ag-Sb. These eutectic/peritectic reactions may also be linked to the enhancement of electrical conductivity previously observed when Ag is added to Ba0.3Co4Sb12. Also, similar beneficial eutectic/peritectic reactions may be available for other systems where conductive particles are added to other antimonides or other thermoelectric systems.