The increasing demand for lightweight electromagnetic wave (EMW) absorbing monoliths, particularly those capable of absorbing both low-frequency and broadband EMWs, presents a significant challenge. While dielectric nanostructured aerogels have demonstrated high potential and advancements, a gap remains in the development of aerogel-based EMW absorbers to achieve effective low-frequency and broadband absorption. Here, we present a multiscale engineering strategy for fabricating aerogel-metamaterial hybrids, addressing key challenges such as broad bandwidth, low-frequency absorption, and high load-bearing capacity. The proposed absorber consists of a simulation-assisted additive-manufactured thin-walled enclosure embedded with graphene/nanocellulose aerogels, which feature an effective conductive network and abundant heterogeneous interfaces. This multiscale design enables exceptional EMW absorption across the entire 2–18 GHz band, achieving 100% bandwidth coverage, with stable performance under wide oblique incidence (up to 60°) and polarization (both transverse electric and transverse magnetic). Furthermore, the absorber exhibits a low areal density of 2.714 kg m−2 and can withstand at least 95 kg of out-of-plane load. These advancements highlight the potential for developing lightweight, novel EMW-absorbing aerogel metamaterials for low-frequency, ultrabroadband electromagnetic compatibility and aerospace applications.