This research paper presents a comprehensive study on the dynamic behaviour of the consistory building in Comune di Sant’Agapito, Italy, through ambient vibration testing and subsequent data analysis. The consistory building, a significant historical structure, was subjected to an ambient vibration test to capture its natural frequencies and mode shapes. Accelerometers were strategically placed to record the building’s response to ambient vibrations. The collected data was then processed using two distinct methods: Fast Fourier Transform (FFT) and Frequency Domain Decomposition (FDD). FFT and FDD were chosen for their complementary strengths in identifying frequency content and extracting modal parameters, respectively. The differences between the results obtained from FFT and FDD were meticulously analysed to understand the advantages and limitations of each method in the context of historical buildings. To validate the experimental findings, a finite element model (FEM) of the consistory building is developed to simulate its dynamic response. The FEM results were compared with the experimental data to assess the accuracy of the model and the reliability of the FFT and FDD methods. This study not only contributes to the understanding of the consistory building’s dynamic characteristics but also demonstrates the efficacy of combining ambient vibration testing, advanced data processing techniques, and finite element modelling.