Vibration energy harvesting using piezoelectric material has received great research interest in the recent years. One important concern for the development of piezoelectric energy harvesting is to broaden the operating bandwidth. Various techniques have been proposed for broadband energy harvesting, such as the resonance tuning approach, the frequency up-conversion technique, the multi-modal harvesting, and the nonlinear technique. A recently reported linear 2-degree-of-freedom harvester can achieve two close resonant frequencies both with significant power outputs, using its unique cantilever configuration. This article proposes to incorporate magnetic nonlinearity into the linear 2-degree-of-freedom system, aiming at further broadening its operating bandwidth. Experimental parametric study is carried out to investigate the behavior of such nonlinear 2-degree-of-freedom harvester. Among different configurations, an optimal configuration of the nonlinear 2-degree-of-freedom harvester is obtained to achieve significantly wider bandwidth. A lumped parameter model for such nonlinear 2-degree-of-freedom harvester is developed, and the results provide good validation for the experimental findings.