Research on green alternatives from agricultural waste as cement substitutes has been significant. Biochar, with unique properties, can improve cementitious composites’ physical, mechanical properties and aiding carbon capture and storage. In this study, cement mortars were fabricated using rice husk biochar (RHB) at varying dosages - 10%, 20%, 30%, and 40% relative to the cement volume. The carbonation curing has been shown to greatly enhance the cement mortar’s compressive strength, with a maximum increase of 82%. However, a higher dosage of biochar resulted in reduced workability and increased permeable pore space. This study indicates that biochar derived from rice husk waste has the potential to be utilized as a substitute in cement mortar, contributing to waste reduction and offers a promising solution for carbon capture and storage.