Onshore wind plays a central role in the renewable energy mix and will be deployed widely across the globe in the coming years. The foundations typically consist of massive reinforced concrete slabs, designed to resist large moment and lateral loads, but of which the response to repeated cyclic loads of very many cycles is still poorly understood. This paper presents the results of a plane-strain centrifuge model test, aimed at evidencing the behaviour of a typical onshore wind turbine foundation to long-term cyclic loading of increasing magnitude. The results highlight the evolution of the accumulated rotation and settlement of the slab with cycle number and the resulting evolution in deformation mechanism from Particle Image Velocimetry (PIV). The test demonstrates that the slab experiences large rotations, close to the maximum allowable requirements from the current design guidelines. This work provides ground for further investigation towards optimal design to enhance the geotechnical performance while reducing the environmental and financial impact of onshore wind turbine foundations.