This study presents a dynamic characterization of a high-rise multistory reinforced concrete building in Santiago, Chile, under different operational conditions. The primary objective is to establish a robust structural system identification baseline for reliable long-term monitoring procedures. Continuous ambient vibration data were acquired over an extended monitoring period, capturing the building’s response to low-amplitude, naturally occurring, and non-intrusive excitations. The dataset was analyzed and compared using output-only operational modal analysis techniques such as SSI and NExT-ERA. A distinctive feature of this study is the integration of data from recorded low-intensity seismic events, which permits a direct comparison between the baseline dynamic properties and those observed during seismic excitations. This comparison aims to facilitate the assessment of the building under different operational conditions, as well as the identification of any nonlinear behaviour induced by transient seismic loading. Moreover, this comparative study facilitates the evaluation of operational variabilities with statistically significant deviations, providing uncertainty quantification of the characterization of any changes in the dynamic properties of the building. The findings not only validate the use of operational modal analysis for a high-rise building but also outline a clear and practical foundation for implementing long-term performance under different operational conditions and seismic loading.