Modern footbridges are often highly sensitive to human-induced vibrations, and evaluating the vibration response to non-stationary excitation remains a key issue in assessing the vibrational serviceability of these structures. This study adopts and extends the Pseudo Excitation Method (PEM) to determine the non-stationary vibration response of a footbridge under random pedestrian excitation by incorporating human-structure interaction (HSI). A moving spring-mass-damper (MSMD) model is employed to capture HSI, while the excitation forces are represented by two spectral models: Živanović’s spectral model (ZSM) and Caprani’s simple spectral model (SSM). These models provide a more accurate representation of intra-pedestrian variability. Results show that the combination of PEM with the SSM allows the calculation of non-stationary vibrations caused by the random pedestrian loads while significantly reducing computational demands compared to Monte Carlo simulations. Furthermore, SSM offers computational simplicity compared to other spectral models, Hence it demonstrates a greater fidelity in modelling intra-pedestrian variability while analysing the response of a footbridge under the influence of HSI.