Geoffroy’s cat is a small Neotropical felid, seemingly abundant throughout most of its range and exhibiting considerable ecological plasticity. In Brazil, the species is restricted to the Pampas, one of the most threatened biomes in the country, where information on its ecology is scarce. Here we report the first assessments of its density, habitat selection, and activity patterns in Brazil. The study was conducted in human-dominated landscape at the extreme south of the country. Using Spatially Explicit Capture-Recapture (SECR) analyses, the estimated population density ranged from 34.54 (±13.51 SE), based on camera trap and radio-telemetry data, to 41.78 (±16.12 SE) individuals/100 km², based only on camera trap data. A Resource Selection Function (RSF) analysis showed that our study population selected sites with native forest and rivers, and avoided areas close to roads, which probably implies avoidance of human contact. Although we observed a slight increase in its nocturnal activity during spring-summer with respect to fall-winter, this population was predominantly nocturnal throughout the year. The use of grasslands and croplands (non-protected areas) was non-uniformly distributed through the hours of the day, whereas native forest was used more uniformly.