The exploration of cost-effective, highly efficient and robust electrocatalysts toward the oxygen reduction reaction (ORR) is of paramount significance for the advancement of future renewable energy conversion devices, and yet still remains a great challenge. Herein, we demonstrate a straightforward one-step pyrolysis strategy for the scalable synthesis of an iron-nitrogen-carbon hierarchically nanostructured catalyst, in which Fe-based nanoparticles are encapsulated in bamboo-like N-doped carbon nanotubesin siturooted from porous N-doped carbon nanosheets ([email protected] NT/NSs). The delicate fabrication of such an 0D/1D/2D integrated hierarchical architecture with encased Fe species and open configuration renders the formed [email protected] NT/NSs with sufficient confined active sites, reduced charge transfer resistance, improved diffusion kinetics and outstanding mechanical strength. As such, compared with commercial Pt/C, the optimized [email protected] NT/NSs catalyst exhibits efficient ORR activity, superior durability and strong tolerance to methanol in KOH medium. More impressively, when assembled as a cathode catalyst in a microbial fuel cell, the [email protected] NT/NSs electrode displays significantly enhanced power density and output voltage in comparison with commercial Pt/C, holding great promise in practical energy conversion devices. What's more, the simple yet reliable synthesis strategy developed here may shed light on the future design of advanced high-efficiency hierarchical architectures for diverse electrochemical applications and beyond.