Archaeological excavations of the PSG-07 earthen mound at Pontal da Barra in Rio Grande do Sul, southern Brazil have revealed the earliest known evidence for the presence of domestic dog (Canis lupus familiaris) in Brazil. This is the first reported pre-Columbian example in the country. Analysis of morphology, morphometry, and dental enamel laminae identified a left maxillary molar 1, left maxillary molar 2 and attached fragments of the maxilla of C. l. familiaris. A direct radiocarbon date on a fragment of the maxilla provided an age range between 1701 and 1526 cal BP (2σ). This is within the range of other dates for the site, which indicate intermittent occupation between 2024 and 1027 cal BP (2σ). Data from carbon isotope analysis indicates a potential marine diet. However, nitrogen isotope analysis values are lower than expected for a marine diet. The sparse records of pre-Columbian C. l. familiaris in the region emphasise the importance of the present work.