The Philippine-style Austronesian voice system (AVS), which serves to identify a single privileged argument leading to the Subject-Only Restriction, is well-known for its highly articulated nature. While the synchronic status of the AVS has been explored extensively, its diachronic development is less clear. This paper fills the gap in our understanding of the development of the AVS while simultaneously exploring the effectiveness of internal reconstruction as a tool of historical syntax. I argue that both voice marking and the nominalizing function of the AVS affixes were already present at the Proto-Austronesian stage. The analysis presented here capitalizes on simple and independently motivated syntactic phenomena: case marking, the shift from prepositions to preverbs, and reanalysis. Based on these features, I show that the AVS developed out of the reanalysis of reflexive markers into markers of intransitivity and out of prepositions incorporated into the verb complex; these two different sources of voice marking explain why the morphological exponents of different voices are differently positioned in the verb form. The proposed reconstruction straightforwardly accounts for a number of AVS properties, including the prominence of arguments promoted to subject position, the Subject-Only Restriction, the existence of various peripheral functions of the voice affixes, the placement of the affixes, asymmetries in their functions, and tendencies in the later development. The historical analysis also has implications beyond Austronesian, in allowing us to to explain the cross-linguistic distribution of adpositions and preverbs and to captures the descriptive facts of a similar morphosyntactic system outside Austronesian: the voice system in Dinka.