An ocean wave energy harvester from the transverse wave motion of water particles is developed by the piezoelectric effects. The harvester is made of two horizontal cantilever plates attached by piezoelectric patches and fixed on a vertical rectangular column. To describe the energy harvesting process, a mathematical model is developed to calculate the output charge and voltage from the piezoelectric patches according to the Airy linear wave theory and the elastic beam model. The influences on the root mean square (RMS) of the generated power from the piezoelectric patches, such as the ocean depth, the harvester location under the ocean surface, the length of the cantilevers, the wave height, and the ratio of wave length to ocean depth, are discussed. Results show that the RMS increases with the increase in the length of cantilevers and the wave height, and decrease in the distance of the ocean surface to the cantilevers and the ratio of the wave length to ocean depth. As a result, an optimum ocean depth is obtained to achieve a maximum RMS at different harvester locations under the ocean surface. A value of the power up to 30 W can be realized for a practical transverse wave with the values of the ocean depth, wave length, wave height and harvester location under the ocean surface to be 10.6 m, 21.2 m, 4 m, and −2 m, respectively. This research develops a novel technique leading to efficient and practical energy harvesting from transverse waves by piezoelectric energy harvesters that could be easily fixed on an offshore platform.