MacCready was born in 2265. He has served as the mayor of Little Lamplight for three years (since he was ten) when he was chosen by the other residents due to his smarts, toughness and the fact that he doesn't take guff from anyone. He has no fear of adults and is a perfect representative. He is belligerent, small (even for his age), very distrustful of adults and willing to blow someone's head off to defend his young charges, but MacCready is also very loyal to those he considers friends.

MacCready came into office in 2274 shortly after the five-minute rule of Princess. According to Sammy, when Princess demanded the title of mayor to be changed to princess, MacCready punched her in the nose and said that the children of Lamplight needed a leader, not a princess. He was then elected to the position of mayor. The child mayor makes regular patrols around the underground settlement, keeping outsiders and potential trouble makers under close surveillance.

During the decade between 2277 and 2287, MacCready ended up marrying a woman named Lucy and had a son with her named Duncan. When he first met Lucy, he lied to her about his occupation, telling her he was a soldier and concealing the fact he was a hired gun. He never told her the truth. At an unknown point in time, feral ghouls killed Lucy while MacCready fled with Duncan. Some time later, Duncan contracted an unknown disease, prompting MacCready to travel to the Commonwealth to find a cure.

He was employed by the Gunners for some time, but left and has ever since been hounded by them for continuing to take jobs in their territory. He is still skilled with rifles and can make precise head shots. When the Sole Survivor meets him in The Third Rail, he's talking with two Gunners. After they leave, he can be hired as a companion for 250 caps (can be persuaded down to 200 or 100, depending on the size of the player's caps purse). This will be given back to the Sole Survivor after completing one of the parts of his quest. After becoming good friends with him and completing his quest; he will give the Killshot perk, which grants a 20% accuracy boost for head shots in V.A.T.S.