This article examines the autobiographical narrative and polemical treatise of a twelfth century Jewish convert to Islam. Samaw'al al-Maghribī's writings contend with the problems of reconciling exilic Jewish identity during the diaspora with the dominant Muslim high culture in which Jews participated. In particular, his autobiography reveals the profound importance for his conversion of his identitification with Muslim history as represented in historical literature that promoted an ideological vision of the past. Similarly, his polemic articulates a critique of Judaism and Jewish religious identity in remarkably historicist terms that associate the integrity of religious culture with an independent political power. Educated in Islamicate scientific and philosophical culture, Samaw'al privileges a culturally defined conception of "reason" over genealogical links and identifies with the political success of Islamic civilization. His writings exemplify the dynamic tension within Jewish exilic identity between conversion and messianism as resolutions to the conflicts of minority status. In choosing conversion, he denied the endless wait for the Messiah as an irrational failure to recognize the judgments of history.