Ordinary Portland cement (OPC) is a ubiquitous construction material and has long been the most prevalent of all man-made concepts. However, the massive demand for OPC is responsible for approximately 7–8% of all anthropogenic CO2 emissions. Substituting OPC with industrial by-products presents a promising avenue for reducing clinker usage and aiding industry decarbonization. However, concerns arise regarding the presence of trace metals, particularly Pb, which can impede early hydration and degrade material properties. Understanding the kinetics of clinker phase dissolution in the presence of Pb is crucial for mitigating these issues. Conventional characterization methods may alter samples and fail to adequately capture underlying reaction mechanisms. To address this challenge, our study employs in-situ X-ray diffraction (XRD) to accurately assess Pb-OPC hydration kinetics in real time. Furthermore, we develop a geochemical model to quantify hydration reactions. This model supplements experimental findings, providing valuable insights into the proposed mechanisms. Overall, our work enhances the understanding of Pb-OPC interactions in cementitious materials, ultimately contributing to more efficient industrial by-product management and sustainable construction practices.