Electrically conductive porous structures are ideal candidates for lightweight and absorption-dominant electromagnetic interference (EMI) shielding. In this review, we summarize the recent progress in developing porous composites and structures from emerging two-dimensional (2D) graphene and MXene nanosheets for EMI shielding applications. Important properties contributing to various energy loss mechanisms are probed with a critical discussion on their correlations with EMI shielding performance. Technological approaches to constructing bulk porous structures, such as 2D porous films, three-dimensional (3D) aerogels and foams, and hydrogels, are compared to highlight important material and processing parameters required to achieve optimal microstructures. A comprehensive comparison of EMI shielding performance is also carried out to elucidate the effects of different assembly techniques and microstructures. Distinctive multifunctional applications in adaptive EMI shielding, mechanical force attenuation, thermal management, and wearable devices are introduced, underlining the importance of unique compositions and microstructures of porous composites. The process–structure–property relationships established in this review would offer valuable guidance and insights into the design of lightweight EMI shielding materials.