Abstract: In-situ alloying has been demonstrated to be an effective method for modifying the microstructure of additively manufactured titanium alloys. In this paper, the influence of trace TiC powder addition on the microstructure and mechanical properties of wire arc additive manufactured Ti-6Al-4V alloy was investigated. The result showed that the trace TiC powder addition reduced the size of columnar β grains and refined the α-Ti phase in the Ti-6Al-4V alloy, and the microstructure was the fine basketweave structure, and the ultimate tensile strength and elongation reached 1029 MPa and 14.8%, which increased by 12.8% and 26.5%, respectively, synergistically improving the strength and ductility of wire arc additive manufactured Ti-6Al-4V alloy. Meanwhile, the microhardness of the deposited alloy was increased to 362.9HV, which was an increase of 11.4%. As analyzed by EBSD, the addition of TiC powder decreased the texture intensity and increased the orientation of the α-Ti phase. The improvement in mechanical properties of the Ti-6Al-4V alloy after adding trace TiC powder was mainly attributed to fine-grain strengthening and solid solution strengthening, where fine-grain strengthening was the main strengthening mechanism. Comparative analysis of the fracture of the tensile specimens of the two deposited alloys showed that the fracture morphology of Ti-6Al-4V alloy exhibited the mixed plastic-brittle fracture, while the fracture morphology exhibited a typical plastic fracture with a mass fraction of 0.5% TiC powder. The potential of TiC powder as a grain refiner for the wire arc additive manufactured Ti-6Al-4V alloys was demonstrated.