The Battle of Arkansas Post, also known as Battle of Fort Hindman, was fought from January 9–11, 1863, near the mouth of the Arkansas River at Arkansas Post, as part of the Vicksburg Campaign of the American Civil War. Confederate forces had constructed a fort known as Fort Hindman near Arkansas Post, Arkansas in late 1862. In December of that year, a Union force under the command of Major General William T. Sherman left for an expedition against Vicksburg, Mississippi, without Major General John A. McClernand because neither Major Generals Henry Halleck nor Ulysses S. Grant trusted McClernand. After Sherman's force was repulsed at the Battle of Chickasaw Bayou, McClernand arrived and took command from Sherman in January 1863.

McClernand led an expedition to capture the Confederate force at Arkansas Post, despite disapproval from Grant. After arriving near the fort on January 9, Union infantry moved into position on January 10. A major Union naval bombardment of the Confederate fort occurred that evening. Early in the afternoon of January 11, McClernand order a major infantry assault, which moved close to the Confederate fortifications. Having suffered through severe artillery fire, white flags of surrender began to appear above the Confederate positions around 16:00 or 16:30, although the Confederate garrison commander, Brigadier General Thomas J. Churchill denied ordering the surrender. There was some confusion as the surrender occurred anyway, as one Confederate brigade commander initially refused to capitulate. Grant was eventually convinced as to the value of the movement against Arkansas Post after the fact, but demoted McClernand to corps command.

When the surrender was completed, 4,791 Confederates had been captured. Partial returns indicate a further 60 Confederates killed and 80 wounded. The Civil War Battlefield Guide place total Confederate losses as 5,004. McClernand reported capturing 17 cannons, 3,000 stands of infantry weapons, and additional equipment. The men lost at Arkansas Post amount to about a third or fourth of the Confederates then in Arkansas. A few hundred men had managed to escape back to Holmes. Union losses were 1,092 men.[28][59] McClernand's force had suffered 1,061 casualties, and Porter 31.

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Grant had originally thought the expedition a waste of time, and had ordered McClernand back to the Vicksburg area as soon as he found out about the Arkansas Post movement. Grant later sent a disapproving letter to Halleck who gave him permission to demote McClernand.  McClernand made plans and orders for a movement against Little Rock, Arkansas, but this was overruled by Grant, who came down the Mississippi to take overall command of the army. Porter and Sherman were able to convince Grant of the military value of the Arkansas Post expedition. Grant later noted that the Confederate force at Arkansas Post could have proved problematic if left untended. On January 18, or 19, the Army of the Mississippi was dissolved, and McClernand became a corps commander under Grant. Part of the battlefield is located within Arkansas Post National Memorial, although 360 acres (150 ha) have been submerged due to river course changes and the construction of the Arkansas Post Canal.