This study investigates lightweight cement-based composites produced with coffee husk (Coffea arabica) residue as a bio-aggregate. The coffee husk was incorporated as a partial substitute (45% in volume) for fine aggregates. Fresh-state properties were analyzed through calorimetric studies, while hardened-state evaluations included mechanical, thermal, and microstructural analyses. Results showed that the lignocellulosic structure of coffee husk delayed cement hydration, which was mitigated by a washing treatment. This treatment significantly reduced extractive content (up to 82%), improving material compatibility with cement matrices. Despite this, the high shrinkage of coffee husk particles led to a weak interfacial adhesion, influencing mechanical properties. The inclusion of metakaolin and fly ash improved thermal performance and reduced clinker consumption. The composites achieved densities between 1281–1339 kg/m3, qualifying them as lightweight materials. Thermal conductivity values ranged from 0.25 to 0.79 W/(m·K), indicating improved insulation potential. Mechanical tests demonstrated compressive strengths of 1.8–2.2 MPa, comparable to other bio-aggregated composites. This research highlights the feasibility of using coffee husk as a sustainable, cost-effective material for lightweight construction applications.