He claimed later to have dreamed of the first transformation scene and saw inside of its horrific details an opportunity to explore the theme of good and evil in conflict which had always fascinated him. He quickly completed a draft of the story, but following criticism from his wife he burned the manuscript. He began again, this time framing the story as an allegory rather than a piece of straight fiction. He worked at a feverish pace to complete it. Stevenson is said to have composed at a pace of almost 10,000 words a day, blistering by any writer's standards, and completed a draft of the novella in only six days. Making this achievement even more incredible is the fact that Stevenson was bedridden at the time and wrote most of the text while propped on his side. He refined the text for several more weeks and it was published in 1886. It was an immediate success, owing to both its imaginative and horrific plot, as well as its deep engagement with religious themes that dominated the era. Mentions of the conflicted protagonist made their way into a number of sermons delivered on Sunday mornings. From the beginning readers clamored to see the good doctor and his grotesque double and the story was quickly adapted for the stage. Just four days before it was set to open in London, Jack the Ripper claimed his first victim. At one point the lead actor was considered a prime suspect. The macabre coincidence would only fuel the reputation of the play and magnify the horror it inspired in audiences.

Stevenson was now established as one of the leading literary voices in Britain. His fiction was becoming increasingly mature and he received praise from some of the leading authors and critics of his day. He was also respected for a large number of poems, articles, essays and a steady stream of the travel writing which had always preoccupied him. In 1888 he set off on another adventure, his most ambitious to date. Along with his wife, stepson and widowed mother, he set out on a chartered yacht for the Pacific Ocean. He spent the next three years touring a number of Pacific islands including Hawaii, Tahiti and New Zealand. He enjoyed unusually good health during the trip and worked steadily on his writing, much of it influenced by his exotic experiences on the islands. During this period of his career Stevenson produced a number of short stories and travelogue set in the South Pacific and these rank among his finest writing. Stevenson had matured into a master of narrative structure and psychological terror. His writing from this period combines page turning story structures with an acute awareness of the anxieties which plague men's minds. These South Seas stories were said to have been a great influence on the young Joseph Conrad.

In 1890 Stevenson purchased a significant piece of land on Upolu, one the Samoan Islands. He settled there with his wife and instantly began to connect with the natives. He went so far as to adopt a Samoan name, Tusitala, meaning "story-teller." Stevenson was sympathetic to the plight of the natives under the control rule of European colonizers. He was often consulted for advice on the situation and became involved in local politics. He wrote passionately about the situation in A Footnote to History and succeeded in getting two colonial administrators recalled. It was clear that he identified more with the Samoan people than with the Europeans he had been raised among.

Stevenson suffered from occasional bouts of infirmity but his health remained remarkably good while on the island.