<p>Rheocasting offers significant advantages in decreasing casting defects and increasing the die’s life compared to conventional high-pressure die casting (HPDC). It has been used to produce aluminum alloy components of vehicles and the housing shells of communication equipment. One major challenge in applying 7075 and other high-strength aluminum alloys in rheocasting is the high tendency toward shrinkage porosity and hot tearing during forming. Refining the <i>α</i>-Al grains in casting is an effective method to reduce shrinkage porosity and hot tearing. The conventional refiner Al-5Ti-B has been used to refine the rheocast <i>α</i>-Al grains, but the aggregation of nucleoid centroids leads to decreased casting ductility. In this work, a TiN_np/Ti hybrid refiner was used to modify the microstructure and mechanical properties of rheocast 7075 aluminum alloy. The microstructure, phase composition, mechanical properties, and fracture surfaces of castings with varying amounts of hybrid refiner were analyzed. The results showed that the hybrid refiner significantly reduced the size and standard deviation of the <i>α</i>-Al grains in both as-cast and T6 heat-treated conditions. It also decreased the tendency for shrinkage porosity to form. Within the additional amount of no more than 0.3 wt.%, the hybrid refiner significantly improved the mechanical properties, especially elongation, of rheocast 7075 aluminum alloy in both as-cast and T6 heat-treated conditions. This work provides an effective method for refining the grains and improving the mechanical properties of rheocast 7075 aluminum alloy.</p>