Electrocatalytic reduction reactions play a crucial role in electrochemical energy conversion and storage technology, which are emerging technologies to ameliorate environmental problems. Spinel oxides are widely explored in electrocatalytic oxidation reactions but have a poor intrinsic ability to reduction reactions, making their electrocatalytic ability less effective. To improve this, defect engineering is a valuable method for regulating the electronic structure and coordination environment. Herein, this manuscript discusses the use of defect spinel oxides in electrocatalytic reduction reactions, including the different types of defects, construction methods, and characterization techniques. It also outlines the various applications of defect spinel oxides in different electrocatalytic reduction reactions. Finally, it goes over the challenges and future outlooks for defect spinels. This review aims to thoroughly explain how defect spinels work in electrocatalytic reduction reactions and serve as a helpful guide for creating effective electrocatalysts.