The photo-depolymerization of polyethylene terephthalate (PET), a polymer of significant industrial importance and environmental impact, was monitored in real-time using a time-resolved diffusion (TR-D) nuclear magnetic resonance (NMR) acquisition interleaved with a ¹H experiment on a benchtop spectrometer. The approach enabled monitoring of the evolution of the diffusion coefficient, molecular mass, and dispersity of the polymer during the process. Additionally, the kinetic information from the ¹H NMR allowed for the identification of the main cleavage sites in the process. This study investigates how benchtop TR-D NMR offers a powerful non-destructive method for real-time monitoring of photo-depolymerization processes and can serve as a valuable tool for polymer degradation studies under flow conditions.