The long-term effect of lime treatment was evaluated on a 2.5% lime-treated experimental embankment after seven years of atmospheric exposure. The evaluation was done by comparison of (i) the mechanical performance of the field sampled specimens with laboratory cured specimens, and (ii) the physicochemical and microstructural properties of the samples from the lime-treated embankment with specimens obtained from an untreated embankment constructed near to it as a reference embankment. An average Unconfined Compressive Strength (UCS) level of 3.29 MPa was measured in the lime-treated specimens sampled from the core of the embankment. This UCS level was found to be comparable to the UCS of accelerated-cured specimens obtained at a laboratory scale. Thus, such levels of UCS can be expected after long-term in-situ curing. Scanning electron microscope images evidenced the contribution of the formation of cementitious bonding towards such UCS evolution in the lime-treated specimen. The persistence of the lime effect within the core of the embankment was confirmed by the presence of a pH greater than 11. However, a relative decrease in the pH and water content was observed in the upper layer compared to the core of the lime-treated embankment. This indicates that the effect of lime was lost in the upper layer under constant soil-atmosphere interaction and due to the development of vegetation roots. Pore structure observations made by Mercury Intrusion Porosimetry (MIP) and Barrett-Joiner-Halendapore (BJH) methods highlight the formation of smaller pores (diameter < 3000 Å) under lime effect. These smaller pores have contributed towards the evolution of suction in the core-sampled specimens of the lime-treated embankment. This has led to the long-term water retention capacity of the lime-treated soil. BJH was able to detect mesopore-formation (25–500 Å) under the lime effect in a more precise manner compared to MIP. The evolution of mesopores was found to be coincident with the development of strength and specific surface area of the lime-treated soil.