<p>Global waste management and cement production are major but largely disconnected sources of greenhouse gas emissions. This Perspective proposes a new circular industrial symbiosis that links anaerobic digestion (AD) of wet organic waste with the production of supplementary cementitious materials (SCMs) from agro-residues. The aim is to cut methane emissions and reduce clinker use through one integrated valorisation system. Although both pathways are widely used on their own, their structural coupling has received little interdisciplinary attention. SCMs such as rice husk ash, palm oil fuel ash, cassava peel ash, and cocoa pod husk ash can replace 5–35% of Portland cement. This substitution avoids roughly 100–300&#xa0;kg of CO₂ per tonne of cement, based on established clinker emission intensities. In parallel, AD of market waste, abattoir waste, and organic municipal solid waste typically yields 50–100&#xa0;m³ of methane per tonne of feedstock under mesophilic conditions. This output corresponds to about 1.0–1.8 t CO₂e mitigation per tonne through fossil-fuel substitution and avoidance of fugitive landfill emissions. The novelty lies in bringing these two mitigation streams into one clustered ecosystem. The system converts high-organic waste into dual assets: renewable methane and low-carbon cement substitutes. Nigeria is used as a representative case to show how this model can operate in a rapidly urbanising, biomass-rich economy, while remaining adaptable to global contexts. When deployed at scale, integrated AD–SCM hubs can deliver substantial lifecycle emission reductions and align with emerging climate-finance and carbon-accounting frameworks. Future research should apply digital-twin-based techno-economic modelling to test scalability across different regulatory, infrastructural, and market settings.</p>