The construction sector is a major contributor to global carbon emissions and energy consumption, particularly due to cement production, which requires substantial investments in carbon capture and storage to meet net-zero targets by 2050. Thus, the need of sustainable alternatives is crucial to reducing environmental impact. Grounded materials, such as excavated earth, present a promising solution due to their low energy demand and widespread availability. Additionally, the reuse of biobased products from agricultural waste as aggregates in concrete mixtures allows the storage of biogenic carbon and may drive local circular economies, particularly in rural areas. The present research evaluates the mechanical and environmental performance of an innovative bio-composite consisting of rammed earth and crushed hazelnut shells. Twelve alternative mix designs with varying percentages of water, gravel, and shells were defined and tested in laboratory to assess physical and mechanical properties. A Dynamic Life Cycle Assessment (DLCA) was conducted to measure the Global Warming Potential (GWP) of each mixture, including the contribution from biogenic CO2. Results were compared with traditional materials (concrete CEM I, concrete CEM II and clay bricks) based on the same functional unit, equal to 1 m2 of wall with variable thickness according to each material’s compressive strength. Over a 70-year lifespan, the mix with hazelnut shells achieved a negative net GWP, demonstrating the potential for climate-positive outcomes.