The study examines the influence of a sloping porous bed on the efficiency of an oscillating water column (OWC) device facing oblique water waves. A vertical, surface piercing, thin plate near a rigid wall approximates the OWC. The system is simulated using a multi-domain boundary element method assuming the linear potential theory. The impact of varying sloping bed structural parameters and influence of the incident wave angle on the performance of the OWC is evaluated and discussed. The significance of this model to act as a breakwater protecting near-shore marine facilities is also highlighted. The OWC efficiency is found to be highly sensitive to the slope of the porous seabed, and seabed porosity is found to stabilize the resonant frequency against changes in water levels. OWCs are found to be more efficient over porous seabeds with higher frictional coefficients and lower values of porosity. The results indicate the optimum values of the sloping bottom inclination, the porosity and the frictional coefficient for the porous sloping bottom that can be used for the design and implementation of an efficient OWC device.