Recognizing climate change’s severity, reducing the construction industry’s greenhouse gas emissions is crucial in material science, architecture, civil engineering, and construction science. Novel bio-based materials like hempcrete are being developed to lessen the environmental impact of construction. Hempcrete, increasingly used in traditional and advanced construction like large-scale 3D printing, is considered carbon-negative due to the biogenic and sequestered carbon of its components. Given the high carbon footprint of Portland cement, hempcrete offers a sustainable alternative for emerging construction technologies. However, hempcrete’s carbon neutrality or negativity depends on the hemp and lime content in the mix. A thorough Life Cycle Assessment (LCA), therefore, becomes important to understand carbon negativity potential of this material. In this paper, we present the results of a cradle-to-gate LCA of hempcrete mixes that have been proposed and examined in empirical studies. The LCA also includes a process-based hybrid cradle-to-gate impact assessment of hemp produced in the United States. The results indicate that the total global warming potential of hemp is roughly −1.72 kgCO2e/kg, and carbon negativity can only be reached with at least 20% of hemp by weight in the hempcrete mix. Findings also show that consideration of carbon absorption of lime binder is essential to reach carbon negativity. Our results further indicate that a balance of carbon negativity and hempcrete’s compressive strength will be more desirable to address both climate change mitigation and adaptation.