This article argues that historians have misread Sir Thomas Smith's famous work as a narrowly factual description of English society and institutions, and Smith himself as a proto-rationalist thinker. Instead, De republica anglorum represents Smith's attempt as a citizen of the elect nation to theorize the ‘mixed monarchy’ inaugurated with Elizabeth's accession. It should thus be read as an important contribution to English Protestant apologetic of the 1560s, in conjunction with the work of men who more obviously engaged in that discourse: John Foxe, Laurence Humphrey, and John Aylmer. The article makes this case by reconstituting three cultural contexts which I argue need to be taken into account when analysing Smith's text. The first establishes Smith's ideological concerns and convictions in Edward VI's reign and in the early years of Elizabeth's. The second focuses on the immediate circumstances in which Smith wrote De republica anglorum: a polemical exchange between the Englishman Walter Haddon and the Portuguese Osorio da Fonseca concerning religious reformation and kingship. I then analyse De republica anglorum with reference to the key terms and issues identified in these contexts. The conclusion locates Smith's text in relation to one further context: Claude de Seyssel's The monarchy of France and its use by French Huguenot theorists in the 1560s. That nexus enabled Smith satisfactorily to address the central problem with which he and fellow apologists grappled throughout Elizabeth's reign: ungodly kingship in the guise of female rule.