A bulk nano-TiC particle reinforced Inconel 625 alloy (TiC/IN625) was manufactured using selective laser melting. The effect of post treatment on the microstructural evolution and mechanical properties of the TiC/IN625 alloy was investigated by using optical microscope, scanning electron microscope, transmission electron microscope, X-ray diffraction, microhardness tests, and uniaxial tension tests. The results demonstrated that heat treatment brought uniformly dispersed γ′ and γ′' phases, coarse MC carbides, and fine secondary carbides to the TiC/IN625 samples. After heat treatment followed by laser shock peening, high-density dislocations and some nanoscale grains were generated in the subsurface of the TiC/IN625 sample. The tensile residual stresses were transformed into compressive residual stresses by laser shock peening. In the laser shock peened TiC/IN625 sample, relatively higher surface microhardness, ultimate tensile strength, and elongation were observed compared to the as-built and heat-treated samples. Furthermore, a synergistic strengthening mechanism, involving precipitation strengthening, grain refinement, and dislocation strengthening, was clearly revealed.