This study explores the incorporation of olive husk, a renewable byproduct of olive oil production, as a sustainable additive in bio-lightweight concrete. Addressing the limitations of raw olive husk in cement-based mortars, both treated and untreated olive husk were introduced at 15% by weight to evaluate their effects on physical, thermal, mechanical, and moisture absorption properties compared to a reference concrete. The results reveal that both treated and untreated olive husk reduce the bulk density of the bio-concrete, increasing porosity by 24% and 26%, respectively. This enhanced porosity significantly improves thermal insulation, with thermal conductivity values of 0.162 W/m·K for untreated samples and 0.692 W/m·K for treated samples. Sorption isotherms indicate that untreated olive husk-based concrete exhibits superior moisture absorption. In contrast, treated olive husk-based samples demonstrate more balanced moisture uptake, offering improved durability under fluctuating humidity conditions. As expected, the inclusion of olive husk results in a reduction in compressive strength, with untreated samples showing a more pronounced decline. Nevertheless, both treated and untreated olive husk maintain acceptable mechanical performance for non-load-bearing applications. Treated olive husk, however, achieves an optimal balance between thermal insulation and mechanical strength, positioning it as a more versatile solution for broader construction use. This research highlights the potential of olive husk, both treated and untreated, as an eco-friendly component in bio-lightweight concrete, contributing to the development of sustainable and thermally efficient building materials.