This species roosts in humid, warm caves, where they often form clusters, sometimes with individuals of other species (Erophylla bombifrons, Glossophaga sp., Mormoops megalophylla, and P. quadridens) (Herd 1983, Gannon et al. 2005). Colonies usually contain a few hundreds to few thousands individuals, but these colonies are not commonly found within caves; thus, this species is only found in 15% of all examined caves in Puerto Rico (Rodríguez-Durán 1998). In Cuba, the species does not show a well-defined exodus from the dayroost, it begins activity early in the evening, 10 to 35 minutes after sunset (Silva-Taboada 1979). Individuals remain active for 5 to 7 hours, then return to the day roost (Baterman and Vaughan 1974). Parnell's Mustached Bat is a fast-flying species that captures its preys in the air. Up to 93% of the bats examined included moths in their diet; other common preys include flies, beetles, ants, grasshoppers, and even dragonflies and damselflies (Gannon et al. 2005).

In its most restricted meaning, this species would be equivalent to populations previously recognized as P. parnellii from the Larger Antilles (Davalos 2006, Clare et al. 2013). This distribution includes Cuba, Jamaica, Hispaniola, and Puerto Rico. Pteronotus parnellii (sensu lato) has been found on the island of St. Vincent in the Lesser Antilles, but the subspecific status of this population has not yet been assessed (Vaughan and Hill 1996).

The species occurs in a number of protected areas throughout its range.