The Siege of Port Hudson began when Union forces, under the command of Major General Nathaniel P. Banks, surrounded the Confederate-held fortifications in Louisiana. Port Hudson was strategically located along the Mississippi River, a vital transportation route for both supplies and troops. The Union aimed to take control of the river, concluding the operations that had began with the capture of Vicksburg. This would effectively split the Confederacy into two parts, hampering their ability to coordinate and supply their armies. The Confederate defenders, numbering about 6,000 troops led by General Franklin Gardner, were well-fortified and prepared for a drawn-out engagement.

As the siege commenced, both sides prepared for a robust confrontation. The Union troops were undersupplied and faced difficult terrain, which made the siege itself arduous. The Confederate forces, on the other hand, had established robust defenses, including artillery positions and trenches that bolstered their position on high ground. Over the following weeks, the siege became a test of resolve and resources, with Union forces bombarding the stronghold and making several assaults, all of which failed due to fierce defense from the Confederates.

As the siege progressed, conditions for the besieged forces deteriorated with shortages of food and supplies leading to desperate measures. Ultimately, after 48 days, the Confederate forces surrendered on July 9, leading to Union control of the Mississippi River, marking a pivotal victory. The fall of Port Hudson, along with the capture of Vicksburg the day before, solidified Union dominance over the river and had significant ramifications for the Civil War, demonstrating the Union's growing strength and strategic capability in the Western Theater.