The development of Ultra-High Performance Concrete (UHPC) opened new research directions for enhancing the architectural design, sustainability and serviceability of concrete structures. However, the costs and resource intensiveness trigger the need for innovative UHPC mix design incorporating alternative materials, such as post-consumption Glass Powder (GP). This works aims at disclosing the microstructure features of UHPGC, in which the constituents can be partially replaced by different fineness of GP without impacting the long-term strengths. By using the latest NI-QEDS technique (coupling NanoIndentation and Quantitative Energy-Dispersive Spectroscopy), as well as image analysis applied to EDS chemical mappings, it was possible to investigate mechanical properties of the microstructure constituents and their volume fractions. A conventional UHPC microstructure was compared to a similar system with 30% replacement of cement by GP and to another system with 50% replacement of silica fume by Fine GP (FGP). The results showed the key role of GP anhydrous particles contributing to the rigid skeleton of anhydrous inclusions, as well as their bond quality with the surrounding cement paste. The reduction of cement and silica fume was thus possible without impairing the micromechanical properties of the hydrates, by improving the particle packing density in the hardened state. As major conclusion, replacing cement and silica fume with GP and FGP without impairing both micro-scale and macro-scale mechanical properties provides a promising means to reduce the environmental footprint of current UHPC mix design.