Efficient yet cost‐effective electrode materials play deciding roles in the widespread application of fuel cells, as precious metals, such as platinum (Pt), remain the main component of the cathodic oxygen reduction reaction (ORR) electrocatalyst. Herein, a type of biomass, macadamia nut shell (MNS), is utilized for synthesizing ORR catalysts, aiming at enhancing the activity and lowering the production cost of the electrode materials. Benefiting from a defective catalysis mechanism, the resulting defective MNS material (D‐MNS‐A) shows greatly improved ORR performance in alkaline solutions. The onset potential of D‐MNS‐A is only 29 mV more negative than that of the commercial Pt/C. Moreover, the durability of D‐MNS‐A is superior to that of Pt/C, and it presents excellent tolerance to methanol. In addition, D‐MNS‐A is an ideal material for supercapacitors. It exhibits a specific capacitance of 155 F/g under the current density of 1 A/g in 1 M Na2SO4 electrolyte, which was further increased to 231 F/g after coating with MnO2. The defective nature combined with the highly porous structure of D‐MNS‐A render it a potential material for fuel cell and supercapacitor applications.