Cement stabilization is a conventional technique utilized for improving soil strength and engineering properties. This method of combining cement with soil and letting it cure for up to a month has demonstrated an increase in strength worldwide. However, the cement’s pozzolanic impact endures for several months to several years. So, the main goal in this study is to understand cement stabilization’s long-term Unconfined Compressive Strength (UCS) behavior in high plastic silt of the lacustrine and fluvio-deltaic deposits within the Kathmandu valley. To illustrate the behavior, disturbed soil samples from a site were air-dried, finely pulverized, and sieved to remove any foreign objects and guarantee the uniform mixture with cement. Using the Harvard Miniature Apparatus, UCS specimens were prepared after variable quantities of cement (2–10%) were added to the soil. The samples were subjected to varied curing (28, 60, and 90-days) and the test was performed. The UCS values of the natural soil after 28 curing days was 270.38 kPa, which is taken as the standard for comparison of other UCS values of the cement treated soil. The results showed an increase in UCS values with the increment of the cement content as well as for a longer curing times. While checking the UCS behavior, soil stabilized with 2–4% cement concentrations showed increased strength from 270.38 kPa to nearly 400 kPa (modified soil after 90 days of curing). The strength increased sharply for 4–6% cement concentration, and then gradually rose from 6 to 10%. So, the ideal cement concentration for stabilizing high plastic silt in the Kathmandu Valley is considered as 6%. After 90 days of curing with 6% cement, the strength gain is 3.3 times greater than natural soil (which was left to cure for 28 days), highlighting the importance of prolonged curing times for improved UCS in cement-stabilized high plastic silt of the valley.