|“||The scum tried to knife me. KILL HIM!||”|
–-Shagrat to the other Orcs
His Uruk-hai tower garrison fought with an Orc patrol from Minas Morgul over possession of Frodo Baggins' Mithril mail-shirt. Shagrat interpreted his orders literally: all captives to be searched, but left unharmed and they and their possessions taken to Barad-dûr. Gorbag, leader of a patrol sent up the Stair of Cirith Ungol to investigate matters, coveted the pretty Dwarf-made armor for himself. As is typical with Orcs, a fight soon developed. Gorbag got the worst of it, though he managed to wound Shagrat in the arm. Their respective followers began fighting also, and slaughtered each other wholesale over the next several hours.
Sam, carrying the One Ring, infiltrated the Tower of Cirith Ungol and soon realized that the garrison was effectively wiped out. Unfortunately, Shagrat managed to get past him carrying Frodo's armor and other personal items and escaped. These items were soon taken to Sauron.
It is possible that Shagrat lived to see the end of Mordor, but just as likely he was either killed in the Battle of the Black Gate or executed for the events which took place when the tower was under his command. His arm was badly injured, and unlikely to heal in the short time before the end of Mordor. He expresses a longing for the "old days" before the return of Sauron to Mordor and the reign of the "big bosses", so it's possible he would be content with Sauron's downfall.
In the film version of The Return of the King it appears the Gorbag character is switched with Shagrat, because in the film he says that the Mithril shirt goes to the tower and explaining Shelob's eating habits. Surprisingly, though, Shagrat escapes with it after saying it's his, even though the Mouth of Sauron still has it. Apparently, Shagrat has gotten over his desire for the mithril shirt (possibly out of fear of Sauron or the Nazgûl) and handed it over to the authorities of Barad-dûr.
Shagrat carried abroad an Orc scimitar and possibly a dagger as Cirith Ungol Uruk-hai do. He uses this to cut down enemies and even other orcs with ease.
In The Lord of the Rings: The Third Age (GBA), he appears as a secret villain who can be unlocked afther the player finishes the evil campaign in hard level.