The bird became scarce due to deforestation and perhaps hunting, but it was thought to have been finally wiped out by a series of cyclones and storms that hit Rodrigues in the late 19th century.

Tafforet's 1726 account had been rediscovered the previous year, and A. Newton noted that it confirmed his assumption that the male would turn out be much more colourful than the female.

[3] In 1876, the Newton brothers noted that they had expected the male would be adorned with a red patch on the wing, but that the absence of this indicated it was immature.

[10] The mandible and sternum were extracted from the female specimen, and subfossil remains have since been found in the Plaine Corail caverns on Rodrigues.

Subfossil remains of Newton's parakeet show that it differed from other Mascarene Psittacula species in some osteological features, but also had similarities, such as a reduced sternum, which suggests a close relationship.

[3][12] Many endemic Mascarene birds, including the dodo, are descended from South Asian ancestors, and the British palaeontologist Julian Hume has proposed that this may also be the case for all parrots there.

Hume has suggested that they all have a common origin in the radiation of the tribe Psittaculini, members of which are known as Psittaculines, basing this theory on morphological features and the fact that parrots from that group have managed to colonise many isolated islands in the Indian Ocean.

[3] The Psittaculini could have invaded the area several times, as many of the species were so specialised that they may have evolved significantly on hotspot islands before the Mascarenes emerged from the sea.

[14] A 2015 genetic study by the British geneticist Hazel Jackson and colleagues included viable DNA from the toe-pad of the female Newton's parakeet specimen.

It was found to group within a clade of rose-ringed parakeet subspecies (from Asia and Africa), which it had diverged from 3.82 million years ago.

[16] To solve the issue, the German ornithologist Michael P. Braun and colleagues proposed in 2019 that Psittacula should be split into multiple genera.

They suggested that Psittaculinae originated in the Australo–Pacific region (then part of the supercontinent Gondwana), and that the ancestral population of the Psittacula–Mascarinus lineage were the first psittaculines in Africa by the late Miocene (8–5 million years ago), and colonised the Mascarenes from there.

[19] The general appearance of Newton's parakeet was similar to the extant Psittacula species, including the black collar, but the bluish grey colouration set it apart from other members of its genus, which are mostly green.

[19] It differed from its Mascarene relatives in some skeletal details, including in that the internal margin of the mandibular symphysis (where the two halves of the lower jaw connected) was oval instead of square-shaped when seen from above, and in that the upper end of the humerus (upper arm bone) was less expanded than in the Mascarene grey parakeet and the echo parakeet.

French artist Paul Philippe Sanguin de Jossigny made two illustrations of this specimen, the only known depictions of Newton's parakeet in life, unpublished until 2007.

As A. Newton observed in his original description, some feathers of the female specimen display both blue and green tinges, depending on the light.

[3] According to Fuller, the green parrots mentioned could also instead have been storm-blown members of Psittacula species from other islands, that survived on Rodrigues for a short time.

[3] Hume and the Dutch orhinthologist Hein van Grouw have also suggested that due to an inheritable mutation, some Newton's parakeets may have lacked psittacin, a pigment that together with eumelanin produces green colouration in parrot feathers.

[20] Tafforet also described what appears to be green Newton's parakeets, but the issue of colouration was further complicated by the mention of red plumage: The parrots are of three kinds, and in quantity ...

is slightly smaller and more beautiful, because they have their plumage green like the preceding [Rodrigues Parrot], a little more blue, and above the wings a little red as well as their beak.

[3]In 1987, the British ecologist Anthony S. Cheke proposed that the last two types mentioned were male and female Newton's parakeets, and that the differences between them were due to sexual dimorphism.

The last bird mentioned had earlier been identified as introduced grey-headed lovebirds (Agapornis canus) by A. Newton, but Cheke did not find this likely, as their beaks are grey.

Fuller suggested the single known male specimen may have been immature, judged on the colour of its beak, and this may also explain the absence of the red patch.

Tafforet also stated that the parrots ate the seeds of the bois de buis shrub (Fernelia buxifolia), which is endangered today, but was common all over Rodrigues and nearby islets during his visit.

The echo parakeet was itself close to extinction in the 1980s, numbering only twenty individuals, but has since recovered, so introducing it to the nearby islands could also help secure the survival of this species.

[22] The Mauritian ornithologist France Staub stated in 1973 that his visits to Rodrigues the previous seven years confirmed the bird was extinct.