The Thin Red Line described an episode of the Battle of Balaclava on 25 October 1854, during the Crimean War. In the incident, around 500 men of the 93rd Sutherland Highlanders led by Sir Colin Campbell, aided by a small force of 100 walking wounded, 40 detached Guardsmen, and supported by a substantial force of Turkish infantrymen, formed a line of fire against the Russian cavalry. Previously, Campbell's Highland Brigade had taken part in actions at the Battle of Alma and the Siege of Sevastopol. There were more Victoria Crosses presented to the Highland soldiers at that time than at any other. The event was lionised in the British press and became an icon of the qualities of the British soldier in a war that was arguably poorly managed and increasingly unpopular.

The Battle of Balaclava, fought on 25 October 1854 during the Crimean War, was part of the Siege of Sevastopol (1854–55), an Allied attempt to capture the port and fortress of Sevastopol, Russia's principal naval base on the Black Sea. The engagement followed the earlier Allied victory in September at the Battle of the Alma, where the Russian General Menshikov had positioned his army in an attempt to stop the Allies progressing south towards their strategic goal. Alma was the first major encounter fought in the Crimean Peninsula since the Allied landings at Kalamita Bay on 14 September, and was a clear battlefield success; but a tardy pursuit by the Allies failed to gain a decisive victory, allowing the Russians to regroup, recover and prepare their defence.