In the film, Old Man Marley was Kevin's neighbor. He was called "the South Bend Shovel Slayer", and was said to have murdered his family and half of the people on the block with a snow shovel back in 1958 by Kevin's older brother Buzz. He was also said to have kept his victims in his garbage can full of salt, and that the salt was supposed to have turned the dead bodies into mummies.
When Kevin heads outside, saying that he is not afraid anymore, he screams upon seeing Marley, turns and runs back inside his house, afraid.
Later, Kevin goes to the drug store, gets a toothbrush and asks the clerk about whether or not it was approved by the American Dental Association. Marley then comes in while Kevin is checking his pockets to see if he had brought enough cash with him to buy the toothbrush. Kevin then looks up, sees Marley and backs away a little before running off while also accidentally taking the toothbrush he was holding with him.
The next night, when Kevin goes to church (after meeting with a fake Santa Claus), he meets up with Marley again, and learns that he's actually a nice guy and a Christian, as well as a parent and a grandparent, and that his salting the sidewalks every night with the snow shovel is actually his duty. Kevin also learns that Marley never murdered his family or half the people on his old block like Buzz claimed, but rather had a fight with them — more particularly, his son. Marley tells Kevin that he came to hear his granddaughter sing, and that he can't come and hear her tonight. When Kevin asked him if he meant he had plans, Marley corrected him, saying that he wasn't welcome — not at the church (as he believes everyone is always welcome at church) — but with his son.
According to Marley, years back, before Kevin and his family moved into the neighborhood, he and his son got into an argument for an unknown reason as a result of losing their tempers, and told each other they didn't care to see each other anymore, causing them to become estranged from each other ever since. Kevin asks Marley to call his son, and Marley says that he's afraid to because he thinks that his son won't talk to him. Kevin tells Marley that he used to be afraid of his basement until he turned on the lights, and that Marley should call his son, and whether or not his son talks to him, Marley will know and he won't be afraid. Kevin tells Marley that he should also do it for his granddaughter, who probably misses him and the presents. Marley tells Kevin that he sent his granddaughter a check for Christmas, and Kevin tells him he wished his grandparents did that, but they usually send him clothes.
Later, after Harry and Marv capture Kevin at the Murphys' house, and Harry is about to bite Kevin's finger, Marley comes in and knocks out both burglars with his snow shovel before taking Kevin back home.
The next day, after Kevin's family returns, Kevin walks over to the window, and smiles upon seeing that Marley had taken his advice and reunited with his son, his daughter-in-law and his granddaughter. Marley looks up and, upon seeing Kevin, smiles and waves to him as a sign of thanking him, and Kevin waves back, smiling still. Finally, Marley turns and goes into his house with his family to spend Christmas with them.
- You can say hello when you see me. You don't have to be afraid.
- There's a lot of things going around about me, but none of it's true.
- (About the church) This is the place to be if you're feeling bad about yourself.
- How you feel about your family is a complicated thing.
- Deep down, you'll always love them. But you can forget that you love them, and you can hurt them and they can hurt you, and that's not just because you're young.
- You're always welcome at church.
- You can be a little old for a lot of things, but you're never too old to be afraid.
- (After hearing about Kevin's experience in the basement) Basements are like that.
- (Smiles) Merry Christmas.
- (While taking Kevin off the hook) Come on. Let's get you home.
- In the novelization for Home Alone, Marley says to Kevin, “You don’t have to be so scared of me. All that stuff you hear about me — none of it’s true. Just the product of someone’s overactive imagination”.