Due to the importance of the authenticity of Egyptian monovarietal Koroneiki virgin olive oil, its special characteristics should be studied. This study aimed to investigate certain compounds to characterize monovarietal Koroneiki virgin olive oil (KVOO) and evaluate its authenticity. The reliable markers, which include fatty acid composition, tocopherols, phytosterols, total phenolic compounds, pigments, and oxidative stability, were determined to obtain a complete picture of this oil. In addition, the characterization of its by-products, such as leaves and pomace, was also evaluated. The monounsaturated fatty acid content in the Egyptian KVOO was the highest (74.46%). The linoleic/linolenic acid ratio (11.17) could be used as proof of the purity of KVOO. It is also characterized by its higher content of α-tocopherol (97.77%). β-sitosterol was the main phytosterol. This oil has unique characteristics of cycloartenol and 24-methylen cycloartenol, which are present in reasonable amounts (14.0 and 13.7%, respectively). It was found that olive pomace extract contains higher total phenolic and flavonoid content than olive leaf extract, which in turn has higher radical scavenging activity. The obtained results demonstrate the unique properties and valuable compounds of the monovarietal KVOO. The KVOO co-products can be used as value-added compounds for some food industries.