The Night Parrot is a critically endangered nocturnal bird of Australia's arid zone. The species was "lost" for most of the 20th century until its rediscovery in 1990. Extant populations are now known in eastern and western Australia, but the species has been extirpated from much of its historical range. Here we estimate critically needed Essential Biodiversity Variables (EBVs) for the Night Parrot from historical and opportunistically collected contemporary samples. We find little population structure across the species' range and evidence of recent connectivity between extant populations similar to 2000 km apart. Most eastern individuals show significant kinship with one another, as did two from an extinct population in southern Australia. Heterozygosity is similarly low in all extant populations but ten-fold lower in the extinct population sampled. Coalescent modelling of effective population size (Ne) suggests that Night Parrot numbers were reasonably high until around 90 years ago when Ne crashed from similar to 10,000 to similar to 100. Current Ne is now at its lowest in the past several million years. Our findings will help guide the ongoing management of one of Australia's most threatened birds.