- "It's my father's sword, and his father before him. The Mormonts have carried it for five centuries. It was meant for my son, Jorah. He brought dishonor to our House... but he had the grace to leave the sword before he fled from Westeros."
- ―Lord Commander Jeor Mormont
Longclaw is a Valyrian steel sword, in the possession of House Mormont for five centuries. When Lord Jeor Mormont retired from his lordship to take the black and command the Night's Watch, he passed it to his son and heir, Ser Jorah Mormont. When Jorah went into exile after trying to sell some poachers into slavery, he had the sword sent back to his father on the Wall.
Years later, Jeor gave Longclaw to Jon Snow as a reward for saving his life from a wight. Before giving it to Jon he had the pommel remade, replacing the bear with a direwolf, the sigil of House Stark.
Longclaw is a bastard sword (also known as a "Hand-and-a-half sword"), which is longer than a longsword, but shorter than a greatsword. Greatswords are so large that they can only be wielded using both hands, preventing usage of a shield. Bastard swords can be used with one or two hands: while they are larger than longswords they are short enough that they can still be wielded with one hand, though it is preferable to use two hands.
Jeor gives the sword to Jon Snow as a reward for saving his life from a wight. Before passing it on to Jon, he remarks that the name "Longclaw" is just as suitable for a wolf as a bear. Mormont has had the pommel remade, replacing the bear with a direwolf, the sigil of House Stark.
Jon takes the sword to the dining hall to get the Lord Commander's dinner. He is confronted by the other recruits. Pyp and Grenn are especially vocal in demanding to see the sword.
Craster briefly takes Longclaw from Jon after the latter follows him into the woods to see what the man does with his baby sons. Jon is admonished harshly by Mormont for this, who returns the sword to him and instructs him not to lose it again.
Jon later takes Longclaw with him when he takes part in the Great Ranging beyond the Wall led by Mormont. Jon is sent with a scouting party led by Qhorin Halfhand which ambushes a group of wildlings, during which Jon takes the young wildling woman Ygritte captive. Qhorin leaves Jon to execute Ygritte with Longclaw, but Jon cannot bring himself to execute a female captive. She tries to run, resulting in both becoming separated from Qhorin's group, and Jon ends up taking her prisoner.
Ygritte, however, later lures Jon into a trap. He is captured by a group of wildlings led by the Lord of Bones, who take Longclaw from him. Ygritte carries Longclaw as they head back to the main camp of King-Beyond-the-Wall Mance Rayder.
As they are about to reach the camp, Ygritte playfully keeps lightly whacking Jon in the head with the flat side of the sword. He eventually dodges and slips behind her, noting that she doesn't know how to wield a sword very well. Qhorin, having also been captured, stages a fight with Jon to convince the wildlings that he is betraying his vows to desert to them, so he can infiltrate Mance Rayder's camp. Qhorin steals a sword from a guard, so Ygritte tosses Longclaw back to Jon so he can defend himself. As Qhorin intended, Jon ends up killing him, impaling him on Longclaw. This marks the first time Jon has ever killed anyone. The wildlings are thus convinced that he wants to defect, and lead Jon into the camp.
Having gained Mance Rayder's trust, Jon is given back Longclaw.
Jon carries Longclaw with him as he climbs back south over the Wall. At Queenscrown, when his true allegiance to the Night's Watch is revealed, Jon fights the wildling company he is with. Jon kills Orell with Longclaw, marking the first time he kills an opponent with the blade (Qhorin's earlier death having been staged).
Jon uses Longclaw during the Battle of Castle Black, killing several wildlings with the bastard sword. In a duel with Styr, the Thenn manages to knock Longclaw out of Jon's hands, but Jon smashes a hammer into his skull and kills Styr. After the battle, Jon intends to find Mance Rayder. Remembering that Jeor told him never to lose the bastard sword again, Jon gives Longclaw to Samwell Tarly for safekeeping.
When the White Walkers attack Hardhome, Jon is able to defeat one in a duel using Longclaw. To both of their surprise, the Valyrian steel sword does not break after coming into contact with the White Walker's ice blade. Longclaw shatters the opponent on contact, revealing that dragonglass is not the only thing that can kill a White Walker.