In this paper, modeling of energy harvesting from transient vibrations of slender wings using piezoelectric transduction is implemented in a strain-based geometrically nonlinear beam formulation. The resulting structural dynamic equations for multifunctional beams are then coupled with a finite-state unsteady aerodynamic formulation, allowing for both energy harvesting and piezoelectric actuation with the nonlinear aeroelastic system. With the development, it is possible to provide an accurate, integral aeroelastic and electromechanical solution of both energy harvesting from and active control for wing vibrations, considering the geometrical nonlinear effects of slender wings. The current paper focuses on modeling the energy harvesting subsystem and exploring its impact on the multifunctional system. Vibrations of a slender multifunctional wing excited by both aeroelastic instability and external wind gusts will be considered as the sources of energy harvesting. All simulations will be completed in the time domain to accurately capture the nonlinear behaviors of the slender multifunctional wing. Based on the time-domain analysis, results of this effort illustrate that the piezoelectric energy harvesting from transient vibrations may provide adequate energy to support onboard sensor operations. In addition, results indicate that a well-tuned piezoelectric energy harvesting system may control the wing vibration using the shunt damping effect.