In pursuit of producing an environment-friendly, lightweight, and thermally insulating cement-based composite, silica aerogel was synthesized from rice husk, which is a commonly available agricultural waste, and incorporated into cement at various ratios. Aerogel-incorporated cement-based composites with aerogel replacing the sand by 25, 50, 75, and 100 vol% were fabricated to study the effects of aerogel content. The synthesized aerogel and cement-based composites were characterized by contemporary material analysis techniques such as XRD, SEM, TEM, BET, and MIP. The porosity, density, compressive strength, and thermal conductivity of the cement-based composites were analyzed and discussed in detail. Aerogel produced from agricultural waste rice husk showed excellent thermal insulation and light weightiness. The density of the aerogel-incorporated cement-based composites was half that of the control samples, while a fivefold decrease was observed in thermal conductivity compared to the thermal conductivity of the control samples. This type of aerogel synthesized from rice husk, which showed comparable or better performance than most studies can pave the way for further research into finding green sources for building materials.