This article analyzes the development of a criminal defense case that took place in Chile's Araucania Region in 2013, and in which a Mapuche man was convicted of femicide. The man's legal defense was provided by the specialized Mapuche Public Defender's office. In this article we examine the legal defense provided to this man, the manner in which the specific socio-cultural conditions were taken into account, the theoretical and methodological frameworks and juridical resources considered in the defense's arguments, and the internal limitations met by said arguments in terms of the judicial conviction. Our analysis covers the defense's actions, the arguments presented by the defense, and the assimilation of exculpatory legal categories and of categories of understanding that are typical of the Mapuche cognitive and medical worldview. This case is especially interesting because it allows us to recognize a specific type of socio-cultural legal defense and to derive lessons that can inform a pluralistic and fair legal theory and practice in multi-ethnic and multi-cultural contexts such as the Chilean society today.