It was founded in 1631 by
Siberian Cossack ataman Ivan Galkin, who built an
ostrog (fort) there. The fort's military importance declined in the latter half of the 17th century; however, the settlement was increasingly important as a river port, becoming one of the main starting points for
trade along the Lena. Mineral springs to the west of the town were reportedly discovered as early as the 17th century by
Yerofey Khabarov and a
spa was built at the site in 1925. In the early 20th century Ust-Kut served as a destination for political exiles, most notably
Leon Trotsky. In 1951, the railway from
Tayshet reached Ust-Kut. The town thus became the first and only river port on the Lena served by the railway and an important railhead through which cargoes could travel to and from the locations along the Lena, such as most of
Yakutia. Ust-Kut was granted town status in 1954, with the merger of the original settlement of Ust-Kut and the river port suburb of Osetrovo. Ust-Kut remained the end of the line until 1974, when construction work started to extend the railway, now known as the
Baikal–Amur Mainline, east toward
Lake Baikal and beyond. The town became the headquarters of the construction of the western section of the BAM. ==Administrative and municipal status==