A novel bianisotropic metasurface (BMS) based beam-switching/steering technique is demonstrated using Fabry-Perot (FP) cavity antenna. The proposed configuration comprises of a patch antenna and the BMS as a partially reflecting surface. The BMS is consisting of strongly coupled two layers of metallic patches, termed as a constant phase layer (CPL) and a gradient phase layer (GPL). Due to the bianisotropic nature, this BMS introduces a direction-dependent asymmetrical reflection phase response when electromagnetic (EM) waves originating from patch antenna are incident on it from two opposite directions. These EM waves undergo a constant reflection phase of π when it impinges on the BMS at the side of CPL results into a directive beam along the broadside direction. Now, BMS is flipped over patch antenna to illuminate its gradient side (GPL) which facilitates beam in the off-normal direction. Furthermore, beam-steering in the E -plane is obtained by slowly rotating the BMS over patch antenna. Therefore, the proposed configuration can switch/steer the direction of main beam in the elevation plane while maintaining its compact configuration (2.4λ 0 ×2.4λ 0 ×0.5λ 0 ). The design parameters and characteristics of the proposed configuration are also obtained analytically using basic theories of the FP cavity antenna and the phased array..