Climate change and the growing carbon footprint of cement-based construction materials have intensified the search for sustainable alternatives. This study introduces a novel approach to producing green concrete by partially replacing cement with minimally processed algal biomass cultivated in brackish wastewater and seawater, alongside mineral carbonate-rich CCS (Carbon Capture and Storage) spent pellets obtained from a direct air capture system. Additionally, brackish water algal biomass was explored as a partial replacement for fine aggregates. The incorporation of algae and CCS pellets into concrete formulations not only reduces reliance on traditional cement but also enables long-term carbon storage within the high-alkalinity environment of concrete (pH 11–13), which minimizes microbial degradation of the embedded biomass. Com-pressive strength tests conducted at 7 and 28 days demonstrated that mixtures containing up to 15% brackish water algae, 10% marine algae (with or without the addition of microsilica and chemical admixtures), or 10% CCS pellets surpassed the 20 MPa strength benchmark required for non-reinforced concrete applications. These findings offer a promising pathway for integrating carbon-negative materials into construction practices while advancing environmental initiatives such as artificial reef development and coastal restoration strategies.