Three-dimensionally (3D) ordered macro-/mesoporous (3DOM/m) materials, which combine the advantages of high surface area of the mesopores, efficient mass transport within the macropores, and strong structural stability of the 3D interconnected porous frameworks, have shown remarkable performances in a wide range of applications. Herein, we demonstrate a novel dual-hard-templating technique as a general synthetic strategy for constructing the 3DOM/m materials by nanocasting mesoporous silica confined within the regular voids of a silica colloidal crystal (opal). Through this method, various materials, such as 3DOM/m Pt, Pd, Ni₂P, carbon and N/P co-doped carbon (NPC), have been successfully synthesized. The as-prepared 3DOM/m Ni₂P and NPC are demonstrated to exhibit outstanding electrocatalytic performance for the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR), respectively. The 3DOM/m Ni₂P exhibits a low overpotential of 92 mV at 10 mA cm⁻² and a small Tafel slope of 41 mV per decade, as well as a long-term durability for the HER in acidic medium. The 3DOM/m NPC exhibits comparable catalytic activity but higher durability in comparison with the commercial 20 wt% Pt/C catalyst for the ORR in alkaline medium. Details on the fabrication and characterization of these materials are presented including scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, nitrogen adsorption, X-ray photoelectron spectroscopy, and electrocatalytic activity studies.