Conductive porous materials having a high surface reactivity offer great promise for a broad range of applications. However, a general and scalable synthesis of such materials remains challenging. In this work, the facile synthesis of catalytic metal nanoparticles (NPs) embedded in 2D metal-organic frameworks (MOFs) is reported as highly active and conductive porous materials. After the assembly of 2D conductive MOFs (C-MOFs), i.e., Cu-3(hexahydroxytriphenylene)(2) [Cu-3(HHTP)(2)], Pd or Pt NPs are functionalized within the cavities of C-MOFs by infiltration of metal ions and subsequent reduction. The unique structure of Cu-3(HHTP)(2) with a cavity size of 2 nm confines the bulk growth of metal NPs, resulting in ultra-small (approximate to 2 nm) and well-dispersed metal NPs loaded in 2D C-MOFs. The Pd or Pt NPs-loaded Cu-3(HHTP)(2) exhibits remarkably improved NO2 sensing performance at room temperature due to the high reactivity of catalytic metal NPs and the high porosity of C-MOFs. The catalytic effect of Pd and Pt NPs on NO2 sensing of Cu-3(HHTP)(2), in terms of reaction rate kinetics and activation energy, is demonstrated.