The eastern brown snake (Pseudonaja textilis), often referred to as the common brown snake, is a species of extremely venomous snake in the family Elapidae. The species is native to eastern and central Australia and southern New Guinea. It was first described by André Marie Constant Duméril, Gabriel Bibron, and Auguste Duméril in 1854. The adult eastern brown snake has a slender build and can grow to 2 m (7 ft) in length. The colour of its surface ranges from pale brown to black, while its underside is pale cream-yellow, often with orange or grey splotches. The eastern brown snake is found in most habitats except dense forests, often in farmland and on the outskirts of urban areas, as such places are populated by its main prey, the house mouse. The species is oviparous. The International Union for Conservation of Nature classifies the snake as a least-concern species, though its status in New Guinea is unclear.

It is considered the world's second-most venomous land snake after the inland taipan (Oxyuranus microlepidotus), based on its LD₅₀ value (subcutaneous) in mice. The main effects of its venom are on the circulatory system: coagulopathy, haemorrhage (bleeding), cardiovascular collapse, and cardiac arrest. One of the main components of the venom is the prothrombinase complex pseutarin-C, which breaks down prothrombin.

John White, the surgeon-general of the First Fleet to New South Wales, wrote, A Journal of a Voyage to New South Wales in 1790, which described many Australian animal species for the first time. In it, he reported a snake that fits the description of the eastern brown snake, but did not name it. French zoologists André Marie Constant Duméril, Gabriel Bibron, and Auguste Duméril were the first to describe the species in 1854. They gave it the binomial name Furina textilis – furine tricotée (knitted furin) in French – from a specimen collected in October 1846 by Jules Verreaux, remarking that the fine-meshed pattern on the snake's body reminded him of fine stockings, which was the inspiration for the name. Due to differences in appearance, different specimens of the eastern brown snake were categorised as different species in the early 19th century. German herpetologist Johann Gustav Fischer described it as Pseudoelaps superciliosus in 1856, from a specimen collected from Sydney. German-British zoologist Albert Günther described the species as Demansia annulata in 1858. Italian naturalist Giorgio Jan named Pseudoelaps sordellii and Pseudoelaps kubingii in 1859.

Gerard Krefft, curator of the Australian Museum, reclassified Duméril, Bibron, and Duméril's species in the genus Pseudonaia [sic] in 1862 after collecting multiple specimens and establishing that the markings of young snakes faded as they grew into adult brown snakes. He concluded the original description was based on an immature specimen and sent an adult to Günther, who catalogued it under the new name the same year when cataloguing new species of snakes in the British Museum's collection. After examining all specimens, Günther concluded that Furina textilis and Diemansia annulata were named for young specimens and Pseudoelaps superciliosus, P. sordelli, and P. kubingii were named for adults, and all represented the same species, which he called Diemenia superciliosa. Belgian-British naturalist George Albert Boulenger called it Diemenia textilis in 1896, acknowledging Duméril, Bibron, and Duméril's name as having priority. In subsequent literature, it was known as Demansia textilis as Diemenia was regarded as an alternate spelling of Demansia.

The brown snakes were moved from Diemenia/Demansia to Pseudonaja by Australian naturalist Eric Worrell in 1961 on the basis of skull morphology, and upheld by American herpetologist Samuel Booker McDowell in 1967 on the basis of the muscles of the venom glands. This classification has been followed by subsequent authors. In 2002, Australian herpetologist Richard W. Wells split the genus Pseudonaja, placing the eastern brown snake in the new genus Euprepiosoma, though this has not been recognised by other authors, and Wells has been strongly criticised for a lack of rigour in his research.

Within the genus Pseudonaja, the eastern brown snake has the largest diploid number of chromosomes at 38; those of the other species range from 30 to 36. A 2008 study of mitochondrial DNA across its range showed three broad lineages – a southeastern clade from South Australia, Victoria, and southeastern and coastal New South Wales; a northeastern clade from northern and western New South Wales and Queensland; and a central (and presumably northern) Australian clade from the Northern Territory. The central Australian clade had colonised the region around Merauke in southern West Papua, and the northeastern clade had colonised Milne Bay, Oro, and Central Provinces in eastern Papua New Guinea in the Pleistocene via landbridges between Australia and New Guinea.

P. textilis is monotypic. Raymond Hoser described all New Guinea populations as Ps. t. pughi based on a differing maxillary tooth count from Australian populations; this difference was inconsistent, and as no single New Guinea population is genetically distinct, the taxon is not recognised. Wells and C. Ross Wellington described Pseudonaja ohnoi in 1985 from a large specimen from Mount Gillen near Alice Springs, distinguishing it on the basis of scale numbers, but it is not regarded as distinct.

The species is commonly called the eastern brown snake or common brown snake. It was known as marragawan to the Eora and Darug inhabitants of the Sydney basin. To the Dharawal of the Illawarra, it is goobalaang. The Dharawal and Awabakal held ceremonies for the eastern brown snake. Warralang is the reconstructed name in the Wiradjuri language of southern New South Wales.