During World War II, British POWs are subjected to the brutal conditions of a Japanese prison camp in Burma. The camp is commanded by the strict Colonel Saito, who orders the prisoners to construct a railway bridge over the River Kwai. The bridge is meant to serve as a vital supply route for the Japanese forces. Amongst the prisoners is the principled Colonel Nicholson, who opposes the poor treatment and exploitation of his men. However, Nicholson takes pride in British engineering and discipline, and sees the construction of the bridge as a way to maintain the morale and spirit of his men. He persuades Saito to let the prisoners build the bridge their way and takes charge of the project, unwittingly aiding the enemy.

Meanwhile, an American prisoner, Commander Shears, escapes the camp, suffering through the jungle before he is rescued and brought to a British hospital. Despite his reluctance to return to the dangers of war, Shears is recruited for a mission to return to the camp and destroy the very bridge that Nicholson's men are building. Three commandos, led by the determined Major Warden, join Shears in this perilous undertaking. As the mission commences, their stealthy approach contrasts with the daily grind of the British prisoners who, under Nicholson’s zealous command, are obsessed with completing the bridge as a monument to British fortitude and ingenuity, unaware of the impending sabotage threat.