Even though there is an abundance of data regarding the reproductive biology and postnatal growth of bats, comprehensive data on life history is still lacking for most species, particularly for rare families that have unique behavioral and ecological adaptations. In this study we provide a description of reproductive seasonality and length of reproductive activities such as gestation and lactation for Thyroptera tricolor, a small (3–4.5 g) Neotropical insectivorous bat and one of only four species in the family Thyropteridae. In addition, we also describe postnatal development, including growth rates and the onset of flight. Our results show that T. tricolor has long gestation (at least 3.5 months) and lactation (4 months) periods within a single annual reproductive event. Young are capable of sustained flight at two months of age, and attain adult forearm length at age 90 days and adult body mass at age 120 days. Offspring mortality was high, with 28% of young dying before age five months. Surviving young remained with their mother and natal group for at least one year. In addition, our field observations suggest that males attained sexual maturity earlier than females, at one year of age, while females became sexually active after their first year. These findings suggest that, among bats, T. tricolor may have an unusually slow life history, which could be attributed in part to its unique roosting ecology and social behavior.