Abstract Single-atom catalysts (SACs) have sparked broad interest recently while the low metal loading poses a big challenge for further applications. Herein, a dual protection strategy has been developed to give high-content SACs by nanocasting SiO 2 into porphyrinic metal–organic frameworks (MOFs). The pyrolysis of SiO 2 @MOF composite affords single-atom Fe implanted N-doped porous carbon (Fe SA –N–C) with high Fe loading (3.46 wt%). The spatial isolation of Fe atoms centered in porphyrin linkers of MOF sets the first protective barrier to inhibit the Fe agglomeration during pyrolysis. The SiO 2 in MOF provides additional protection by creating thermally stable FeN 4 /SiO 2 interfaces. Thanks to the high-density Fe SA sites, Fe SA –N–C demonstrates excellent oxygen reduction performance in both alkaline and acidic medias. Meanwhile, Fe SA –N–C also exhibits encouraging performance in proton exchange membrane fuel cell, demonstrating great potential for practical application. More far-reaching, this work grants a general synthetic methodology toward high-content SACs (such as Fe SA , Co SA , Ni SA ).