The construction sector is under intense pressure to become more sustainable due to the significant CO₂ emissions coming from cement production. A key strategy is the extensive use of alternative binders in substitution of pure cement clinker. In this regard, Limestone Calcined Clay Cement (LC³) shows great promise due to its easy adaptability on current technology. This study focuses on lightweight cementitious materials based on LC³, integrating foam and recycled carbon fibres (rCF) from end-of-life Fibre-Reinforced Polymers (FRP). The aim is to enhance the mechanical properties and foam stability as well to promote circularity. The resulting Fibre-Reinforced Foamed LC³ (FRFLC³) mix was developed to achieve a lower material density that is suitable for lightweight applications in civil engineering. The primary objective was to compare the fundamental properties (workability, density, flexural strength, and compressive strength) of foamed mix without rCF, which was considered the benchmark, and the FRFLC³ mix in their fresh and hardened states. The results confirmed that the addition of rCF successfully enhanced the mechanical properties of the composite and improved its workability for extrusion. Furthermore, preliminary extrusion trials demonstrated that the FRFLC³ mix had a satisfactory strength-to-density ratio and exhibited excellent print quality.