A completely coupled piezoelectric-mechanical theory which includes the nonlinear piezoelectric effects is developed for composite plates with embedded or surface bonded actuators and sensors. A higher order laminate theory is used to describe the displacement field in order to accurately capture the effects of transverse shear in moderately thick laminates. The coupling between the piezoelectric effect and mechanical response allows for mutual influence of multiple actuators and transformation of energy between the electrical and the mechanical fields. A new fourth order distribution of electric potential is used to develop an electrical model completely compatible with the assumed higher order strain field. The behavior of actuators subjected to large electric fields is captured using the nonlinear piezoelectric-mechanical coupling terms. The resulting model shows good correlation with available experimental data.