This paper reports the demonstration of an ultra-low power MEMS-CMOS oscillator for strain sensing, powered by a miniature piezoelectric vibration energy harvester (VEH). The employment of the Pierce oscillator topology in a MEMS-CMOS oscillator allows for minimisation of the power requirement to as low as 1.1 µW under ideal conditions. A VEH prototype, developed with hard PZT on a stainless steel substrate (∼0.4 cm3 practical operational volume), is able to deliver a typical average power of 187 µW at 11.4 ms−2 and 514 Hz. Some of the practical challenges associated with the integration of the harvester and the MEMS sensor have also been explored, which helps to lay the foundation for realising net-zero-power strain sensors.