Graphene ohmic losses notably hinder the efficiency of graphene-based terahertz (THz) devices. Hybrid metal–graphene structures have recently been proposed to mitigate this issue in a few passive devices, namely waveguide and Vivaldi antennas, as well as frequency selective surfaces. In this work, such a technique is extensively investigated to optimize the radiation performance of a THz Fabry–Perot cavity leaky-wave antenna based on a hybrid metal–graphene metasurface consisting of a lattice of square metallic patches interleaved with a complementary graphene strip grating. Theoretical, numerical, and full-wave results demonstrate that, by properly selecting the unit-cell features, a satisfactory trade-off among range of reconfigurability, antenna directivity, and losses can be achieved. The proposed antenna can find application in future wireless THz communications.