Two-dimensional noble metal-based nanosheets with high porosity represent a class of promising electrocatalysts due to their highly open structure feature, increased atomic utilization efficiency and thus boosted electrocatalytic performances. Nevertheless, it still remains greatly challenging to fabricate highly porous metal nanosheets through a feasible and general approach to date. Herein we present a novel coordination polymer (CP)-engaged approach to create a class of porous 2D Pd nanosheets for enhancing the electrocatalysis of small molecules through a two-step topotactic conversion reaction. The pre-synthesized Hofmann-type CP square nanoplates are firstly converted into Pd-Ni oxide through a mild calcination and eventually transformed into Pd porous nanosheets after repetitive cyclic voltammetry (CV) treatments in H2SO4 solution. Benefiting from intriguing structural advantages, the formed porous Pd nanosheets exhibit greatly improved catalytic performance toward the electrooxidation of liquid fuels (e.g., CH3OH and HCOOH) and oxygen reduction reaction (ORR) as compared with commercial Pd black catalyst. The present synthetic strategy would provide a new perspective for the rational fabrication of noble metal-based porous nanosheets with extraordinary functionalities.