The microorganism-rich nature of the ocean imposes great challenges to the structural integrity of metals over their service lifespan, including titanium (Ti) alloys, which are usually prone to microbiologically influenced corrosion (MIC). So, multifunctional anti-MIC Ti alloys need to be developed and studied. This paper investigates the effect of copper (Cu) concentration on the MIC resistance of a series of additively manufactured, ultrafine-grained Ti-xCu (x= 3.5, 6.5 and 8.5 in wt.%) alloys. The dependence of the corrosion resistance and MIC resistance on the Cu concentration of Ti-Cu alloy is interpreted considering all conceivable mechanisms. The mechanisms for excellent corrosion resistance of Ti-Cu alloy in seawater are attributed to the strong passive film and small surface potential difference between phases. Microstructural characterization reveals that uniformly distributed, nanosized Ti₂Cu phase led to increased reactive oxygen species in the bacterial membrane, which is the root reason for the superb anti-bacterial property (99.2%) for Ti-8.5Cu. Compared to pure Ti and Ti-6Al-4V, Ti-8.5Cu alloy features both high strength (yield stress > 1000 MPa) and the best MIC resistance (97.5%). The combination of such balanced properties enables this functional 3D printed Ti-Cu alloy to become an ideal material for load-bearing applications in the marine environment.