Uglúk was stationed at Isengard on January 18th, T.A. 3019, when messengers from Moria reported to Saruman that the Fellowship had passed through Moria and were heading south. Saruman then sent a group of scouts under the control of Uglúk to bring back the Hobbits. Uglúk was not told of the One Ring but he was aware that the Hobbits had a weapon that was wanted for the war.
On the fourth day, January 22nd, Uglúk's group reached Moria and they gathered together a force of mountain Orcs. On January 24th they captured Gollum who later escaped. Uglúk sent word to Isengard and Saruman sent him reinforcements. Uglúk's army began to grow as they now had over 80 Uruk-hai and over 100 Orcs from the Misty Mountains. Saruman ordered Uglúk to "Kill all but NOT the Halfings; they are to be brought back ALIVE as quickly as possible ... Alive and as captured; no spoiling.". (The Two Towers)
On February 6th, Uglúk and his company searched northern Rohan for the Fellowship. On the 10th Uglúk met an Orc from Mordor named Grishnákh to the north of Sarn Gebir. Grishnákh's troops guarded the eastern side of the River Anduin while Uglúk's troops watched the western side. However Uglúk was soon ambushed by Rohirrim and forced to retreat to Emyn Muil.
The two met up again on February 25th in west Emyn Muil. The next day they found Meriadoc Brandybuck and Peregrin Took in the woods on the slopes of Amon Hen. Boromir came to their defense but was slain and the Orcs took the Hobbits captive. Grishnákh wanted to take the halflings to Mordor, but Uglúk refused as his orders were to bring them to Isengard. When two others began arguing, Uglúk cut off their heads which prompted Grishnákh to back down and leave the group.
As they marched back to Isengard, a scout named Snaga spotted a Rider of Rohan in the distance. Uglúk became enraged that the horseman had been allowed to escape and raise the alarm. He gave Merry and Pippin an Orc-draught and forced them to run at a faster pace.
The Orcs from the Misty Mountains feared the Rohirrim and they attempted to flee to Fangorn Forest but the Uruk-hai overtook them. Grishnákh and a bank of Mordor Orcs rejoined Uglúk and told him that he intended to ensure the orders were carried out with regards to the prisoners.
On the evening of February 28th, the Rohirrim surrounded Uglúk's company on a hill near Fangorn Forest. Uglúk ordered not to attack as he anticipated reinforcements led by Mauhur to be coming. He ordered for Merry and Pippin to be guarded and not killed unless the Riders broke through the defenses.
Grishnákh disobeyed Uglúk's orders and took the Hobbits away to search for the One Ring but he was slain by a Rider. Merry and Pippin then escaped.
Mauhur's reinforcements arrived but they were defeated by the Rohirrim. At dawn on February 29th, the Rohirrim attacked Ugluk's company. Uglúk managed to hold together a band of his followers and tried to escape into Fangorn, but they were eventually overtaken and killed. Uglúk fought Éomer, the leader of the Rohirrim, sword to sword but he was defeated and Éomer slew him.
- The Two Towers, "The Uruk-hai"
- The Lord of the Rings: A Reader's Companion, "The Departure of Boromir,", "The Uruk-hai,"