He was originally a farm boy at the Gift, but flees to the Night's Watch after his village is attacked by wildlings and later fights alongside Jon Snow in the Battle of Castle Black. He eventually becomes a true member of the Night's Watch and is named as Jon's steward when Jon is elected the new Lord Commander, but ultimately betrays and fatally stabs Jon during the Mutiny at Castle Black after believing that Jon is showing mercy to his family's killers.
Olly lived with his mother and father in a village at the Gift.
When Olly and his father are on their way home for dinner, their village is attacked by a group of wildlings. When his father is killed by Ygritte, his mother tells him to hide. He flees, and she is killed by Styr. Olly hides under a cart, but is caught by the Thenn warg. The warg brings him to Styr, who holds a blade to his throat. Styr tells Olly that he is going to eat his dead parents, and orders him to tell the men of the Night's Watch at Castle Black in an attempt to draw them out into the open. He then releases Olly, who reaches Castle Black and informs the men of the approaching wildlings.
Olly stays at Castle Black, living amongst the brothers of the Night's Watch and wearing the black clothes of the Night's Watch. He later trains with them for the upcoming fight against the wildlings. Olly brags to the brothers about his archery skills, though only Grenn says he believes him, as well as promising to take him hunting soon.
Olly greets Jon Snow, Grenn and Eddison Tollett as they return to Castle Black after coming from Craster's Keep. Jon pats him on the head as he greets the brothers.
During the Battle of Castle Black, Olly is assigned to work the wooden lift system. As the battle rages on Samwell Tarly urges him to pick up a weapon and defend himself. Olly then spots Ygritte preparing to kill Jon Snow. Before she can shoot Jon, Olly uses a bow to kill Ygritte with an arrow through the heart, avenging his father in the process. After the arrival of Stannis Baratheon and his forces, Olly is among the black brothers that attend when the fallen brothers are burned in Castle Black's courtyard.
Olly remains at Castle Black and spars with Jon Snow in the training yard, alongside other new recruits. He has little experience with a sword and shield, but Jon does his best to teach Olly how to be a proper swordsman. Olly abruptly stops sparring when Melisandre arrives to fetch Jon. Later, Olly is present when Mance Rayder is executed by Stannis Baratheon for refusing to bend the knee.
Olly is present at the choosing for the 998th Lord Commander of the Night's Watch and is happy when Jon Snow defeats Ser Alliser Thorne for the position of Lord Commander.
Jon later names Olly as his personal steward, grooming him for command as Jeor Mormont once did for him. He is present at Jon's meeting with Stannis Baratheon and Davos Seaworth, in which Jon points out, while looking at Olly, that many of his black brothers do not like the wildlings. Later, Davos asks Olly to recite part of the Night's Watch oath in order to persuade Jon to rally the Night's Watch to Stannis's side in the upcoming battle for the North. Olly is later at a meeting of Night's Watch where Janos Slynt refuses to man and repair Greyguard, a ruined castle on the Wall. Jon orders Slynt to be brought outside and orders Olly to bring him Longclaw. Olly gives Jon his sword and witnesses Slynt's execution.
However, Olly's trust in Jon begins to sour after Jon makes the suggestion of allowing the wildlings to pass through the Wall and become subjects of the Seven Kingdoms or even members of the Night's Watch so as to avoid them falling into the coming White Walker army. First Steward Bowen Marsh points out what the wildlings did to Olly's family and friends in the Gift while in Mance Rayder's army. Later, in Jon's office, Olly asks if Jon means to lure the wildlings into a trap, but Jon denies it, reminding Olly that despite the losses they have suffered at the wildlings' hands, they will need all the help they can get if the Night's Watch is to stand a chance against the White Walkers.
Later, Olly visits Sam in his rooms, ostensibly to offer him some food. However, he wants to ask Sam why Jon would want to join forces with the Wildlings, particularly Tormund, who led the raid in which his parents were killed. Sam reassures Olly that Jon knows what he is doing, and that unless he is successful, neither the Night's Watch nor Westeros stands a chance against the White Walkers. Sam explains this is a hard choice Jon had to make, however unpopular, and then then tells him not to worry, as Jon always comes back.
When Jon Snow returns from Hardhome with thousands of wildlings and lets them in through the Wall, Olly is among the many black brothers who look at the wildlings and even their Lord Commander with disgust. When Jon smiles at Olly, the boy goes away angrily.
Olly is sent to Jon's room to let him know that a Wildling knows where his uncle Benjen is. Jon quickly rushes out of the room, across the courtyard and past a group of Night's Watchmen, only to find a sign with the word "Traitor" scrawled upon it. Several Night's Watchmen mutiny against Jon and stab him, bringing him to his knees, and Olly approaches. Jon whispers Olly's name as a plea for mercy. With tears in his eyes, Olly finishes Jon off by stabbing him through the chest, ending the mutiny and leaving his Lord Commander dead in the snow.
Olly is present in the dining room of Castle Black when Thorne announces Jon's murder at their hands and gives his justification to sway most of the Watch to his side. He witnesses Thorne issue Davos Seaworth and the brothers loyal to Jon his ultimatum to surrender or die.
Later, Olly is present as the mutineers attempt to break into the room where Jon's body is. Before the mutineers can break in however, Edd returns with Tormund Giantsbane and an army of wildlings. Though Thorne demands that the watchmen stand and fight, they are intimidated into surrender by the giant, Wun Wun. Olly then charges Tormund(Likely due to his involvement in the attack on Olly's village), but is quickly defeated and disarmed. Then, Olly, along with Thorne and the officers who mutinied alongside him, are led away to the Ice Cells.
After Jon Snow's resurrection and subsequent reclamation of command, Olly is led to the gallows to be publicly hanged for treason. As Jon asks his condemned murderers for their last words, Olly refuses to speak and instead glares furiously at Jon. After a moment of silence from Jon, Olly gives him one final look of hatred before he is hanged along with the others.
Young Olly joined the Night's Watch after witnessing the murder of his parents by Tormund and his band of wildlings. He avenged his parents' death by killing Ygritte during the Battle of Castle Black. Olly served as steward to Lord Commander Snow, but felt betrayed by Jon's pact with the wildlings. He conspired with other brothers to murder him, and delivered the fatal cut. After Jon's resurrection, the Lord Commander oversaw Olly's execution.