Fire-damaged concrete often suffers from severe strength loss and poor bond performance, while conventional Portland cement repairs have high carbon footprints and limited thermal compatibility. This study investigates geopolymer mortars incorporating fly ash, GGBFS, nano-silica, polypropylene fibres, and recycled aggregates (RA; 0–100%) as sustainable post-fire repair materials. Specimens were exposed to 400–800 ℃, followed by air or water cooling, and tested for compressive, slant shear, and pull-off adhesion performance. A simplified life cycle assessment quantified embodied CO₂ per MPa of recovered strength as an integrated sustainability–performance index. Results show that the 50% RA mix (M2) achieved 42.9 MPa compressive strength and 4.94 kg CO₂/MPa, balancing structural recovery with a 47% lower carbon footprint than OPC controls. Higher RA content improved environmental efficiency but reduced strength and bond capacity. This dual-performance framework demonstrates that moderate RA substitution in geopolymer mortars offers a scalable, low-carbon, and thermally resilient repair strategy for fire-exposed concrete infrastructure.