This paper presents an indirect impact-based piezoelectric vibration energy harvester using a freely movable metal sphere as a proof mass and an MFC (Macro Fiber Composite) beam as a piezoelectric cantilever. The impact of the spherical proof mass and both end walls of the channel generates MFC cantilever vibration in response to low-frequency external vibrations such as human-body-induced motion. Size and position of the proof mass on an MFC beans have been optimized to generate higher output power effectively. A proof-of concept device has been designed, fabricated and tested using vibration exciter. An analytical model has been developed by examining the behavior of indirect impact system and MFC cantilever. Moreover, the vibration mode of the MFC cantilever has been analyzed with finite element analysis and frequency domain analysis. With the developed model, theoretical open circuit voltage has been compared with experimental results. Maximum peak-to-peak open circuit voltage of 42.2 V and average power of 633.7 mu W have been obtained at 3 g acceleration at 17 Hz. Long-term reliability of the device has been verified by cyclic testing. After the measurement of fundamental characteristics, we have proposed a new device with improved output performance which generated maximum average power of 963.9 mu W at 3 g acceleration at 18 Hz. To improve the long-term reliability, a modified device with titanium alloy housing has been fabricated, which provided 11.9% power decrease after 489,600 cycles of operation.