Nanotechnology, originally developed for high-tech applications, is increasingly being applied in the concrete sector. Among its various applications, it provides a cost-effective solution to accelerate early-age compressive strength development, a critical requirement in precast concrete production, without increasing environmental impact or compromising the long-term durability. This study investigates the use of a C-S-H-based admixture to improve the economic and environmental sustainability, as well as manufacturing efficiency, of precast concrete. A conventional precast mixture was optimized by gradually reducing the cement content by up to 60 kg/m3, while incorporating the seeding admixture. The experimental investigation included adiabatic calorimetry, compressive strength tests from 16 h to 28 days, and simulations of environmental impact and production costs. The results demonstrate that the optimized mixtures achieved both early-age and long-term compressive strength targets, even with significantly lower cement content. Moreover, the optimized concretes exhibited a lower carbon footprint and production costs comparable to the reference mixture. These findings support the adoption of nanotechnology as a scalable and sustainable strategy to reduce the carbon footprint of precast concrete production.