The Siege of Port Hudson, Louisiana, (May 22 – July 9, 1863) was the final engagement in the Union campaign to recapture the Mississippi River in the American Civil War.

While Union General Ulysses Grant was besieging Vicksburg upriver, General Nathaniel Banks was ordered to capture the lower Mississippi Confederate stronghold of Port Hudson, in order to go to Grant's aid. When his assault failed, Banks settled into a 48-day siege, the longest in US military history up to that point. A second attack also failed, and it was only after the fall of Vicksburg that the Confederate commander, General Franklin Gardner surrendered the port. The Union gained control of the river and navigation from the Gulf of Mexico through the Deep South and to the river's upper reaches.