This study demonstrates the synthesis of nanosilica aerogels (NSAs) from waste glass using a CO₂-based extraction process. The process was optimized by varying key reaction parameters, including extraction temperature, reaction duration, NaOH concentration, and waste glass fineness. The resulting silicate precursors, which demonstrated high CO₂ capture efficiency, were used to prepare NSA particles. The synthesized NSA exhibited an extremely high surface area and porosity; thus, these can be used as a value-added, lightweight, and reactive supplementary cementitious material for producing thermally insulating concrete. The incorporation of NSA accelerated hydration, with nucleation and pozzolanic effects contributing to 21% and 3%, respectively, to the hydration process. The initial hydration acceleration was attributed to the extremely high surface area of NSA, which facilitated the precipitation of hydration products on its surface. At later stages of hydration, the pozzolanic reaction of NSA promoted the formation of calcium silicate hydrate (C-S-H) in the cement matrix. This reaction increased the chain length of the C-S-H gel, resulting in a more robust and interconnected gel network. The densification effect mitigated potential mechanical property losses caused by the porous nature of NSA. Additionally, the porous structure of NSA significantly reduced the matrix density, leading to lower thermal conductivity and improved insulation performance. This study presents a new approach for valorizing recycled glass, promoting CO₂ sequestration, and producing high-value aerogels for use as additives in the development of lightweight insulating concrete.