This paper addresses the problem of the experimental characterization of cement-treated compacted soils in terms of microstructural, hydraulic, and mechanical properties. Tests were conducted on two different types of soil: silty sand and clay as fine soils, and gravelous sand and alterite as granular soils. Samples were mixed with 5% cement and compacted at different levels (i.e., 85, 95, 100, and 105% of the maximum dry density, respectively, as achieved using the standard compaction method). The results of the mercury intrusion porosimetry (MIP) tests performed on these cement-treated soils revealed significant changes regarding macropores. A reduction in both size and volume due to the combined effects of treatment and compaction was observed in fine soils, and an even higher reduction was seen in granular soils. Because the permeability was mainly governed by the macropores, a decrease in the permeability was clearly observed for all tested soils when the degree of compaction increased. This decrease was significantly greater in fine soils, which were more sensitive to compaction effects than granular soils. Unconfined compressive strength (UCS) results showed that the addition of cement improved UCS values due to an increase in cohesion. The cohesion increase was generated by the cement bonding and enhanced by the compaction effect. Based on a recently developed approach, a prediction model for the permeability of cement-treated compacted soils was proposed. Microstructural and compaction characteristics were taken into account. This original predictive model considered the treatment effects on both the pore interconnection and the morphological parameters of the pore structure (i.e., constrictivity and tortuosity).