Biochar has emerged as a promising material for carbon sequestration and decarbonization efforts. By capturing atmospheric CO₂, biochar contributes to reducing greenhouse gas concentrations and enhancing environmental sustainability. Grout, essential in concrete structures, plays a significant role in determining the mechanical and durability properties of concrete. Understanding the impact of biochar on grout can lead to advancements in sustainable construction materials. This study evaluates the effect of incorporating biochar on the fresh and hardened properties of grout, such as flowability, consistency, and compressive strength at 1, 3, 7, and 28 days. Rheological assessments were conducted using tests such as the mini slump test, Lombardi plate test, and Marsh cone flow time, while compressive strength tests were performed to assess mechanical performance. The results indicate that biochar incorporation increases water demand, but this can be effectively mitigated with higher water-to-binder ratios and superplasticizer dosages. Optimized biochar mixes exhibited excellent flowability, with mini slump and Marsh cone values comparable to control mixes. In terms of compressive strength, mixes with moderate biochar replacement (2.5–5%) and proper adjustments in mix design achieved superior performance, with strengths exceeding 100 MPa at 28 days. These findings demonstrate that biochar can enhance grout sustainability without compromising mechanical or fresh properties, paving the way for greener construction materials.