Piezoelectric cantilever devices for energy harvesting purposes have typically been tuned by manipulating beam dimensions or by placement of a tip mass. While these techniques do lend themselves well to designing a highly tuned resonance, the design is fixed and causes each system to be unique to a specific driving frequency. In this work, we demonstrate the design of a nonlinear tuning technique via a variable external, attractive magnetic force. With this design, the resonance of the piezoelectric energy harvester is able to be tuned with the adjustment of a slider mechanism. The magnetic design uses the well of attraction principle in order to create a varying nonlinear stiffness, which shifts the resonance of the coupled piezoelectric beam. The significance of this work is the design of a piezoelectric energy harvesting system with a variable resonance frequency that can be adjusted for changes in the driving frequencies over a wide range without the replacement of any system components; thus, extending the usefulness of these vibration energy harvesting devices over a larger frequency span.