Converting ambient vibration energy into electrical energy is a potential technology for powering wireless sensor networks (WSNs). In this paper, an electromagnetic vibration energy harvester (EVEH) based on a diamagnetic levitation system is proposed for harvesting energy from ultralow-frequency, broadband vibration sources. In this design, a diamagnetic levitation structure is utilized to reduce the operating frequency, and mechanical impact is effectively introduced to broaden the working bandwidth. A simulation model of the energy harvester is built to illustrate the energy conversion process. The performance of the energy harvester is experimentally investigated under harmonic excitation with different acceleration levels and frequencies. At an acceleration of 1 g, a maximum peak-to-peak voltage of 370 mV is measured over a wide frequency range of 3–16 Hz, and the root mean square (RMS) output power at the optimal resistance is obtained as 26.7 μW at the excitation frequency of 6 Hz. In addition, the real-time characteristic of the proposed energy harvester is explored by harvesting energy from human motions such as hand shaking, stepping, and jumping. Compared with recent diamagnetic-levitation-based vibration energy harvesters, the harvester can be efficiently operated in an ultralow-frequency, random, and large-amplitude-vibration environment.