This study aims to propose a coupled controller of tuned mass damping (TMD) and nonlinear energy sink (NES) for enhancing the stability and suppressing nonlinear vibrations of slender structures, such as tall buildings subjected to cross airflows. The nonlinear governing equations are established to describe the coupled vibrations of the slender structure with the controller. Subsequently, a linear analysis is performed to indicate the positive effect of proposed controllers on increasing the onset speed of galloping for the slender structure. A nonlinear analysis is conducted to state the mechanism of controllers on reducing oscillations of the slender structure. The results show that the coupled controller has better effects on whether enhancing the onset speed or oppressing the structure’s vibration amplitudes. A parametric analysis is then carried out to design an optimal coupled controller. The distributed controllers are designed in the structure, indicating that there is an optimal number for the controller where the onset speed is peak depending on the mass ratio. The present study can provide beneficial guidance and design for controlling the cross-flow-induced vibrations of slender structures in engineering applications.