Among the diversity of solid waste produced, biomass by-products stand out due to their synergizing role in energy savings during brick firing process and impact on mitigating sustainability issues of fired clay brick production. Therefore, this study accentuates on assessing the characteristics of fired clay bricks made by replacing clay with both biomass bottom ashes (BBA) and spent charcoal from 8 to 20 wt% in order to minimize non-renewable resource use and enhance brick performance. In total, bricks from 6 mixture series were prepared to ascertain the effect of 5 wt% BBA incorporation and 3 – 15 wt% spent charcoal addition on the physical, durability, mechanical and thermal properties of the produced fired clay bricks. Parameters such as linear shrinkage, dried weight, dried and fired apparent densities, water absorption, open porosity, thermal conductivity and compressive strengths were examined at spent charcoal increasing inclusion in the brick bodies. The produced bricks showed linear shrinkage values within the safe limits of 7%. Water absorption values were also within acceptable levels of 16.33%. Thermal conductivity significantly reduced from 0.76 W/mK to 0.58 W/mK and this reduction meant improvement in the thermal efficiencies of the bricks. Bricks containing 5 wt% BBA and 9 wt% of spent charcoal exhibited compressive strengths of 10.40 MPa in accordance with standards required for structural construction. These results were authenticated from mineralogical and microstructural analyses. Consequently, utilization of up to 20% wastes in a brick body is a crucial step in point of economic growth, environmental cleanliness, natural clay resources conservation and innovation in the fired clay bricks product development.