Sleepy is first introduced, with his six companions, at the Dwarfs' Mine. He controls the mine cart, presumably transporting the diamonds to Doc, who then sorts them. The cart is pulled by a deer. At one point the fly pesters Sleepy, who in an attempt to swat it accidentally hits the deer's backside; this causes the deer to kick the cart several times, sending Sleepy flying. As the dwarfs march home, singing "Heigh-Ho", Sleepy is fourth in line. He is the only other dwarf beside Dopey not to join in the singing, as he is too tired.
When the seven dwarfs reach their cottage, they think that a monster has taken up residence in their house. They sneak into the cottage (Dopey peeking through Sleepy's beard) and search the room. The dwarfs note that the cottage has been cleaned. They decide that whatever is in the cottage is upstairs, and Doc declares that one of them must go upstairs to chase it out of the house. Dopey is elected, and Doc, his hand shaking, gives Dopey the candle. Dopey is so terrified upon entering the bedroom that, when he hears a noise coming from the beds, he screams and rushes downstairs. The other dwarfs think that he is the monster and rush outside, locking the door. Dopey falls into the kitchen and emerges from the cottage covered in pots and pans. When the other dwarfs see him they, thinking that he is the monster, start hitting him. When they realize that it is Dopey, they decide to venture into the bedroom. They are about to strike whatever is sleeping in their beds when they realize that it is the princess, Snow White. Grumpy begins to complain, and Doc attempts to silence him, but Snow White is woken up. She manages to match the name at the foot of each bed to the correct dwarf, identifying Sleepy third.
Eventually, it is agreed that Snow White will clean and cook for the dwarfs if she is allowed to stay. She prepares soup for them but demands that they wash first. The dwarfs reluctantly march outside. Here, the dwarfs, led by Doc, when Sneezy dips his finger in the water, he blubbers shocking Sleepy and the other dwarfs except for Grumpy, wash themselves, while singing "Bluddle-Uddle-Um-Dum (The Dwarfs' Washing Song)". Next to Sleepy, the fly can be seen washing on the soap. Grumpy refuses to wash, but the other dwarfs, led by Doc, to drag him to the water and wash him thoroughly. Later that evening, after supper, the seven dwarfs entertain Snow White with "The Silly Song"; to begin with, Sleepy is once again bothered by the Fly, and attempts to hit it with a cymbal, succeeding only in striking himself in the process. After they finish the song, the dwarfs listen to Snow White sing "Some Day My Prince Will Come", which sends every dwarf, except the stubborn Grumpy, into a dream-like state. Doc declares that Snow White will sleep in the bedroom upstairs, and the dwarfs must sleep downstairs. As Sleepy settles down next to the fireplace, where Grumpy is sleeping in the kettle, the fly sleeps on his nose.
The next morning, as each dwarf leaves, he is kissed by Snow White. While the dwarfs head to the mine, the Queen, as the Witch, makes her way to the cottage, knowing that only Snow White will be at home. Upon her arrival at the cottage, the animals sense danger and, after attempting to drive her away, rush to the mine to fetch the dwarfs, where they try to warn them. When Sleepy suggests that the Queen has found Snow White, the dwarfs rush home to find that the Witch has succeeded in poisoning the princess and is about to leave. The dwarfs chase the Witch into the mountains, and she reaches a cliff. She attempts to crush the dwarfs with a boulder, but a flash of lightning causes her to fall from the cliff and be crushed by the boulder herself.
The seven dwarfs mourn Snow White's death; Sleepy, Bashful, and Sneezy are shown silently weeping. The dwarfs found her to be so beautiful, even in death, that they fashion a coffin from glass and place her inside. The Prince arrives, and the dwarfs part so that he can approach Snow White. He kisses her, breaking the spell of the Sleeping Death, and the dwarfs cheer. Before Snow White leaves with the Prince, she kisses each dwarf on the forehead (Sleepy was never shown being kissed on the forehead, but possibly was last).