Degradation of poly(vinyl chloride) is a widely discussed topic, and its thermal stability is one of its most important properties. This work uses coupled thermogravimetric analysis-potentiometric titration for simultaneous analysis of sample weight loss and quantification of released hydrogen chloride. The thermal stability point of highly plasticized samples cannot be determined from thermogravimetric measurement alone, as the weight loss derivative change is not clearly visible. This problem is solved by the presented method, which was applied to both unplasticized and plasticized samples. The obtained data can be used to identify the thermal stability point and separate the mass loss caused by the released hydrochloric acid and by other compounds. Such data can be used in the future for determination of more precise parameters for degradation kinetics models.