The railway's origins lie in the aftermath of the Russo-Japanese War. When the 1905 Treaty of Portsmouth split Sakhalin at the 50th parallel, Japan began building railways across its southern half, Karafuto Prefecture. The first 42.5-kilometer line connected the port of Korsakov to Toyohara, the colonial capital now known as Yuzhno-Sakhalinsk. By 1921, branch lines reached Nevelsk, Kholmsk, Chekhov, and Tomari along the western coast. The network eventually stretched over 1,225 kilometers, all built to the Japanese standard gauge of 1,067 millimeters -- Cape gauge, narrower than the 1,520-millimeter broad gauge used across the Russian Empire and later the Soviet Union. When Soviet forces took control of all Sakhalin after World War II, they inherited a complete rail system they could not connect to their own.

Rather than immediately rebuild, the Soviets adapted. They re-gauged mainland wagons to fit the narrow tracks and commissioned the Lyudinovo locomotive factory to build diesel engines specifically for the island's unique gauge -- the TG16 and TG21 models, machines designed for a railway that existed nowhere else in the Soviet network. In a twist of pragmatism that transcended Cold War politics, trains were also imported directly from Japan: purpose-built A1 sets from Hitachi and Teikoku Sharyo in the late 1950s, followed by D2 sets from Fuji Heavy Industries in 1986, and secondhand KiHa 58 railcars purchased from the privatized Japanese National Railways in the early 1990s. The Soviet era extended the network northward to a peak of 2,500 kilometers by 1992, though closures of underused lines had reduced it to 2,025 kilometers by 2006.

The dream of physically connecting Sakhalin to the mainland has haunted Russian planners for decades. Under Stalin, construction began on a tunnel beneath the Strait of Nevelskoy using Gulag forced labor between 1950 and 1953. The project died with Stalin. Since 1973, a train ferry between Vanino and Kholmsk has served as the only rail link to the continent, a crossing that depends on weather and ice conditions. In 2008, President Dmitry Medvedev proposed a bridge rather than a tunnel, and in 2013 the Russian government formally included a Sakhalin link in federal transport plans -- a 16-kilometer bridge across the strait's narrowest point, plus 925 kilometers of new mainland track to reach the Baikal-Amur Mainline at Komsomolsk-on-Amur. The estimated cost: 21 billion rubles. There have even been proposals to extend a line from Sakhalin's southern tip to Hokkaido via a 40-kilometer bridge or tunnel, which would create a continuous rail link from Tokyo to Europe.

The practical solution, in the end, was simpler than a bridge. Beginning in 2003, Russian Railways undertook the enormous task of converting the entire Sakhalin network from Japanese Cape gauge to Russian broad gauge, re-laying every kilometer of track to accommodate standard Russian rolling stock. The work took sixteen years. In August 2019, the conversion was formally completed, and by the end of September 2020, the last narrow-gauge service had run. The Sakhalin Railway, once the only isolated narrow-gauge network in Russia, was finally compatible with the continental system -- even though no physical connection to the mainland exists. New RA3 diesel railcars now run the same routes that Japanese-built trains once served, and a D51 steam locomotive from the Japanese era sits preserved outside the Yuzhno-Sakhalinsk railway station, a relic of the century when Sakhalin's rails spoke a different mechanical language than the rest of Russia.