Biomaterials and raw earth have demonstrated a promising potential for improving various thermal properties of plastering mortars used in buildings. The objective of this research was the evaluation of the thermal-energy performances and life cycle greenhouse gas (GHG) emissions of different mixtures of engineered, bio-based earth mortars composed of bamboo particles, earth, and different cementitious materials. Four mixtures were assessed: mortars without bamboo particles (matrix), and mortars containing 3%, 6%, or 9% of bamboo particles by volume. The bulk density and thermal conductivity values obtained for the matrix and mortars with the highest percentage of bamboo particles (9%) were 1704.13 and 1471.80 kg/m³, and 0.62 and 0.43 W/M·K, respectively. Based on experimental results, thermal-energy simulations were carried out using a social housing project as a case study. The simulations evaluated different climate conditions and applied life cycle GHG emissions assessment methodology. Compared with typical cement and lime plastering mortars, the proposed bio-based earth mortars presented a superior thermal-energy performance and lower GHG emissions, particularly the 9% bamboo particles mixture. GHG emissions reached a maximum decrease of 28%. The main scientific contribution of this research is the presentation of an engineered, bio-based earth mortar that can be manufactured using local raw materials available in most developing countries with significant housing demands. The method used, based on experimental research, thermal-energy analysis, and life cycle GHG emissions, may be used for evaluating other innovative materials. It was verified that even with thin plastering in buildings, it is possible to achieve energy efficiency gains and to reduce GHG emissions.