This paper presents a systematic design of a piezoelectric stack energy harvester from human walking locomotion. The proposed footstep energy harvester is a mobile energy harvesting device that comprises of four sets of piezo-electric stack with force amplification frame assembly with associated power electronics. The objective of this work is to optimize the output power from each piezo-electric stack for which a high-efficiency force amplification frame was developed. Considering the nature of the application, High-Strength A514 Alloy Steel was chosen as the frame material and SONOX SP 505 as the piezo-electric stack in d33 configuration. The mathematical formulation of real-time human walking force excitation was also vital in the study. In this paper, a real-time equation of human Vertical Ground Reaction Forces (VGRF) was used for the systematic modeling and simulation process. Following the success of piezoelectric electro-mechanical modeling and simulation, a prototype of four sets of force-amplification frames each with a piezoelectric stack installed inside were fabricated and assembled into a unique constrainer box such an assembled device was fit into the heel of a 12 Field and Stream boot to effectively convert kinetic energy from walking locomotion to electricity and therefore, to power a wireless sensor. The uniqueness of the work is to develop an easy-fit footstep energy harvester with much higher power density than similar design in the literature. In particular, the developed energy harvesting device is not visible externally and does not affect the walking gait pattern of the user. Moreover, our design only adds 0.25 kg to the self-weight of 0.85 kg of the boot. A peak power of 130 mW and peak Voltage of 118 V was recorded for an 80 kg person walking. This type of energy harvester will find its application in clean-energy generation in remote areas without electricity access.