Geoffroy's bat has a wingspan of 220 - 250 mm and a distinct notch on its brown ears. Its wooly and dense dorsal fur is tricoloured (grey, rust brown and red), while yellow and grey are present in its venter.
This species can be found in hardwood forests and is considered a cave-dwelling species, despite often roosting in buildings. M. emarginatus males tend to hibernate alone and females form maternity colonies that in average include 200 individuals.
While foraging, Geoffroy's bats tend to avoid open spaces. Instead, they prefer to hunt spiders, moths, lacewings and Diptera through foliage gleaning techniques.
M. emarginatus is regarded as relatively sedentary as its winter and summer roosts are usually less than 40 km apart. However, longer distances (e.g. 105 km) have been recorded.