This Research Note starts by evaluating Lofland and Stark’s conversion model. By comparing it with several radicalisation models, it was found that conversion and radicalisation processes have much in common. Based on this observation, the idea of a radical-conversion model is formulated. Subsequently, five hypotheses derived from the radical-conversion model are tested with a sample of foreign fighters database (n = 408). It was found that converts and non-converts can be seen as equals. The convert’s involvement in suicide missions and perceived trustworthiness are relatively the same as non-converts. However, due to certain predisposition factors, differences for rank, desertion, and the role of women were found. This Research Note suggests that there are strong indications that radicalisation is a sub-type of conversion and that more research is needed on this topic.