In this report, we examine the intricate details of the mechanism driving Zr/CuO thermite system, shedding new light on the exceptional reactivity of Zr fuel with oxygen. Magnetron-sputtered Zr/CuO reactive multilayers were deposited, and thermo-physical techniques were employed to characterize the progression of the chemical reaction upon heating. Unlike commonly used Al fuel, Zr/CuO exhibited 100% heat release below 500 °C, contrasting with the ∼5% observed for conventional Al/CuO system. This enhanced reactivity at low temperature is attributed to the rapid oxygen consumption behavior of Zr, due to the poor barrier of ZrOx to oxygen diffusion. The oxidizing behavior of Zr was quantitatively analyzed using electron microscopy and spectroscopy. Our observations reveal a three-step process of Zr oxidation facilitated by a rapid reduction of CuO to metallic Cu accompanied by the formation of an intermediate Cu2O phase: (i) a preliminary low-temperature mass transport initiating at 275 °C, (ii) partial Zr oxidation forming ZrO2 and oxygen enriched Zr and finally (iii) complete conversion to zirconia at 450 °C. Finally, Zr/CuO reactive thin-films demonstrated a very high reactivity with an ignition delay time of 0.04 ± 0.016 ms and a burn rate of 3.5 m.s−1, in stark contrast to the same volume of Al/CuO, which failed to ignite and burn altogether. This study not only deepens our comprehension of Zr-based thermite system but also underscores its potential for diverse applications in energetic materials.