Baikal Cossacks were cossacks of the Transbaikal Cossack Host (Russian: Забайкальское казачье войско), a Cossack host formed in 1851 in the areas beyond Lake Baikal (hence, Transbaikal).

The Transbaikal Cossack Host partially consisted of Siberian Cossaks, Buryats, Evenkian (Tungus) military units and peasant population of some of the regions. The army included three cavalry regiments and three unmounted brigades. Its main purpose was to patrol the Sino-Russian border and perform everyday military duties. Nakazny ataman (the one who was appointed) was in charge of the Transbaikal Cossack Army. He would also serve as a military governor of the Transbaikal oblast with its headquarters in Chita, starting from 1872.

In the early 20th century, the Transbaikal Cossack Host normally supplied 1 polusotnya of guards (50 men), 4 cavalry regiments, and 2 batteries in the times of peace. During the World War I, it supplied 1 polusotnya, 9 cavalry regiments, 4 batteries, and 3 reserve sotnyas (100 men). In 1916, the Cossack population of the Transbaikal Cossack Host numbered 265,000 people, out of which 14,500 men served in the military.

The Transbaikal Cossack Army is known to have participated in the suppression of the Boxer Rebellion in 1899-1901, Russo-Japanese War of 1904-1905, and World War I. During the Russian Civil War, the more prosperous Cossacks joined the ranks of the anti-Soviet armies of General Grigory Semenov and Roman Ungern. The poorer Cossacks took active part in the guerrilla movement.

In 1920, by the end of the Russian Civil War, the Transbaikal Cossack Host was disbanded.