This article analyzes the evolution of ethnographic texts written about Jê-speaking peoples of the interior of Minas Gerais, Brazil, from the 1760s through the 1830s. It interprets both the timing and content of these sources with reference to the emergence of Enlightenment thought, the development of a transatlantic community of letters, and the intervention of an idiosyncratic French military officer, Guido Marlière, who participated in Brazil’s Botocudo War of 1808–31. Marlière’s writing, informed by his long association with Jê peoples, mastery of their languages, and advocacy for more humane indigenous policy, was unprecedented in its cultural specificity. Marlière also contributed directly and indirectly to the production of canonical texts authored by European scientists. In this article, Bieber recovers Marlière’s vivid, humanizing observations about Jê peoples and uses him as an example of how local actors contributed to the circulation of ideas and production of ethnographic knowledge.