To reduce greenhouse gas emissions (GHGs) and preserve freshwater resources, this study assessed the techno-economic feasibility of utilizing waste streams from natural gas combined cycle (NGCC) power plants to cultivate algae, reuse process waters, and produce hydrogen via hydrothermal gasification (HTG) of algae biomass. Algae cultivation trials indicated that Chlorella vulgaris can be grown in NGCC wastewaters and that the effluent is suitable for industrial reuse. Aspen Plus process simulations showed that the HTG of algae biomass is not economically competitive and that HTG methane emissions must be abated to enable low-carbon hydrogen production. A feasibility analysis of an NGCC-integrated algae cultivation-gasification system (ACGS) concluded that it would be challenging to implement the ACGS due to the high capital and operating costs of the current technology. Further investigation of algae-treated water for NGCC applications and the optimization of HTG processes is recommended to identify a sustainable model for ACGS implementation.