Manipulating particles using a fluid interface has both fundamental implications and technological promises. However, the stabilization of interfacial particle structures remains challenging. This study proposes a room‐temperature particle cross‐linking strategy achieved by introducing a surface transition process to metal particles confined at a liquid metal–electrolyte template, which is electrochemically reducing. The method enables cross‐linking Cu nanoparticles into nanoporous networks of micrometric thickness. It is shown that the particle networks possess remarkable mechanical strength and can be readily isolated and then be transferred onto desired substrates. The electrical properties of the material due to network formation are further highlighted, with a focus on an anomalous electric‐field‐induced resistance reduction effect. Such favorable mechanical property and intriguing conducting behavior forecast promising perspectives of the material for smart sensor applications or novel electronic devices. Meanwhile, the proposed particle cross‐linking method can provide general implications for particle‐based, interface‐assisted fabrication.