The cut-in wind speed and the power output are the two main concerns of a galloping energy harvester. A good galloping energy harvester is expected to have a low cut-in wind speed and a high power output. This paper proposes a two-degree-of-freedom (2-DOF) galloping-based piezoelectric energy harvester (GPEH) by mounting a secondary beam onto a primary piezoelectric cantilever beam. An experimental study is conducted to evaluate the actual energy harvesting performance of the proposed 2-DOF GPEH. The effects of the secondary beam length and the mounting position on the cut-in wind speed and the power output are investigated. It is revealed that the introduction of the secondary beam can reduce the cut-in wind speed from 2.372 m/s to 1.961 m/s. Mounting the secondary beam further away from the bluff body weakens the influence of the secondary beam on the energy harvesting performance of the 2-DOF GPEH. Moreover, the power output can be increased or decreased by tuning the secondary beam length. The power output from a well-tuned 2-DOF GPEH can be increased for about 111.1%, as compared to the conventional 1-DOF GPEH. By contrast, the power output from a badly tuned 2-DOF GPEH is reduced for about 22.2%. A simple theoretical model is developed for explaining the experimentally observed phenomenon and can be used to provide some guidelines in the design of 2-DOF GPEH to avoid performance deterioration.