Throughout its life-cycle, wood contributes to climate change mitigation through carbon storage and material and energy substitution. Focusing on wood use for piles, check dams, paved walkways, guardrails, and noise barriers, we quantified the nationwide potential for climate change mitigation in civil engineering in Japan through 2050. To assess mitigation potential, we examined life-cycle greenhouse gas (GHG) emissions that are avoided by storing carbon in wood and forests, substituting wooden materials for non-wooden materials (cement, concrete, steel, and asphalt), and substituting processing residue and waste wood salvaged from defunct civil engineering structures for fossil fuels (heavy oil). Our projections suggest that there will be a maximum potential domestic log volume of 6.80 million m³/year available for civil engineering use in Japan in 2050, and that it would be possible to produce this volume while increasing Japan’s forest resources over the long term. A maximum nationwide avoided GHG emissions potential of 9.63 million t-CO₂eq/year could be achieved in 2050, which is equivalent to 0.7% of Japan’s current GHG emissions. The breakdown of avoided emissions is 73%, 19%, and 8% for carbon storage, material substitution, and energy substitution, respectively, with the greatest contributions coming from carbon storage through the use of log piles.