Saccolaimus mixtus forages over open eucalypt woodland and forest. It appears to be relatively common in the larger tracts of Eucalyptus tetrodonta forest on the western side of Cape York, but could feasibly roost in any area with larger trees. It is also associated with large river systems. While it has been collected once from a limestone cave in Papua New Guinea (Tate 1941), it usually roosts in tree hollows. It has been recorded roosting in dead E. tetrodonta stags in small groups of two to seven individuals (J. Broken-Brow unpublished data). It forages over canopy, but will also fly underneath and amongst the canopy. Its echolocation call is very similar to that of S. saccolaimus, which limits the ability to distinguish these two species acoustically, but pulses are often a different shape and of higher frequency compared to S. flaviventris. 

Saccolaimus mixtus was first described from three specimens collected near Port Moresby, Papua New Guinea in 1878 (Troughton 1925; curated by the Australian Museum, Sydney). Only two other specimens from near-coastal lowland areas (0-100 m in elevation) have been collected from Papua New Guinea—in the National Capital District (one individual; Queensland Museum, Brisbane) and Western Province (one individual; American Museum of Natural History, New York)—with possibly two others (specimens at the University of Papua New Guinea and Natural History Museum, London) (records on GBIF http://www.gbif.org/species and OZCAM http://ozcam.org.au/; Bonaccorso 1998). It has not been seen in Papua New Guinea since at least 1973 (record from Natural History Museum, London). Most of the remaining 26 or so specimens have been collected from the northern part of Cape York Peninsula, Queensland, Australia. A survey by Reardon et al. (2010) found evidence of its presence via capture, spotlight observations and putatively attributed echolocation calls at several localities in the northern half of Cape York Peninsula and speculated that it could be present further south as well. Its presence on islands in the Torres Strait (Thomson et al. 2008) needs confirmation. Other capture records are available from the western side of Cape York Peninsula (K.N. Armstrong unpub. data).

Saccolaimus mixtus occurs in several protected areas on the Cape York Peninsula, as well as the Tonda Wildlife Management Area in Papua New Guinea. Further research is required on basic biology, in particular habitat and roosting preference, plus some quantification on how much habitat of various vegetation communities is covered by mining tenements, and an estimate of population size. In Papua New Guinea, it should be targeted during research and environmental assessment surveys—with high mist nets and acoustic lures likely to increase the chance of capture.