He passed the bar four years later but would never practice law in his lifetime.

Rather, Stevenson dedicated himself to the two strongest forces in his life, an insatiable wanderlust and his chronic health problems. Throughout his time in college Stevenson traveled prodigiously. Every summer he would make a tour of the Scottish isle with his father to inspect their family's historic engineering projects. Stevenson found the structures themselves boring, but the sights and sounds of his travels provided ample material for his growing imagination. He made frequent trips to urban and rural France in order to indulge his need for culture and climates more forgiving to his ailing lungs. During one of these adventures he took an extended canoeing trip with his friend Sir Walter Simpson. This voyage would be the subject of his first real published book, An Inland Voyage, released in 1878.

It was on this voyage that Stevenson had a fateful meeting with the woman who would later become his wife. Fanny Vandergrift Osbourne was then a married mother of three who had fled to France out of frustration over her husband's infidelities. Osbourne was ten years older than Stevenson but made a powerful impression on the young man. Soon after their first meeting he published an essay called "On Falling in Love." The two became lovers in France while Osbourne was still legally married, but in 1979 she decided to return to her home in San Francisco. Overcome with sadness at her absence, Stevenson ignored the advice of his friends and traveled to America for the first time. It is emblematic of his personality that he took second class passage in order to observe how the common man traveled and increase the adventure of his transatlantic voyage. He then took a train to California, a voyage which would provide fodder for his writing but which would also ruin his health. He arrived in California on the brink of death. He was nursed back to health by the recently divorced Osbourne and in 1890 the two were married. The new couple honeymooned in an abandoned mining camp north of San Francisco, an experience Stevenson would write about in The Silverado Squatters.

Stevenson was now supporting himself and his family with his writing, and occasional cash infusions from his father. But his health remained the most pressing issue in his life. For the next seven years he would travel ceaselessly looking for a locale which would alleviate his lung condition. In spite of his poor health and constant resettlement, Stevenson managed to produce most of his best known works during this period. Treasure Island began as a casual amusement to distract his stepson on a trip to a dreary Scottish cottage. He would admit later that his writing process was guided entirely by the entertainment of himself and his stepson. If they were not engaged, the story was changed. The book, Stevenson's first piece of fiction, was first serialized in a popular boy's magazine. It would go on to be published in book form in 1883 and would become an immediate bestseller. Stevenson's contemporaries were initially confused by Treasure Island. They knew Stevenson primarily as a travel writer and literary critic and could not make sense of his sudden foray into books for boys. Despite its commercial success, the novel could not rise above the label of "children's literature" and Stevenson would make efforts later in life to distance himself from the book. Regardless, the success of Treasure Island established Stevenson as an entertaining new British writer with a flair for romantic adventure.

The idea for what is probably Stevenson's best known story, Strange Case of Dr. Jekyll and Mr. Hyde, came to him one night in a dream.