Current methods to assess the vibration serviceability of footbridges often overlook complexities of the pedestrian-structure interaction. This may result in a discrepancy between predicted and actual structural responses, and cause comfort problems or even structural failure. This study aims to model and calibrate the interaction using high-quality experimental data. Tests involved an average pedestrian walking at a regular pace on the UniOvi laboratory footbridge. This facility features a mechanism that allows easy variation of the footbridge’s mass and stiffness, enabling the study of the system’s vertical vibration across a range of natural frequencies. The footbridge is modelled as a single degree of freedom system that describes its principal vibration mode, and the pedestrian as a single degree of freedom linear oscillator. The dynamic properties of both the structure and the pedestrian are calibrated in the time domain based on the footbridge’s response from free vibration tests. The properties are then fitted to polynomials that depend on the footbridge’s natural frequency. The resulting two degree of freedom model is employed to obtain the structural response spectrum as a function of its natural frequency, which is validated near resonance through data acquired on steady state tests. The validation suggests the model is suitable for reproducing the footbridge’s response.