While traveling through rural Ireland, Porky Pig is caught in a storm and asks for lodgings at a nearby castle, but the caretaker tells him that no one inhabits the place but himself and the leprechauns. Porky dimisses the remark, but then accidentally hits his head and loses consciousness. At that point, "O'Toole" is revealed to be a pair of leprechauns disguised as a human being. O'Pat, the first one, is very nervous and thinks Porky is after their pot of gold. O'Mike, the second leprechaun, convinces his partner that he knows how to deal with the Pig. When Porky wakes up, he is helped to a room by a "reunited" O'Toole who, during the short trip to the room, gets accidentally divided in two again. As Porky notices, he mentions to the top half of O'Toole that he has lost his lower half, and realizing that "O'Toole" is actually two leprachauns, is terrified and runs and hides in his bed, which happens to be a trap door leading to a shaft where Porky drops until he falls into the witness chair in a courtroom. There the Leprechauns find him guilty of trying to steal the pot of gold and sentence him to the wearing of the Green Shoes.
At first Porky appreciates them as some nice shoes, but soon he realizes that they are cursed, as his feet begin a frantic Irish jig. Porky realizes that the shoes will not stop dancing, and even when he removes them, they chase him and return themselves to his feet, and he is "danced" through a nightmarish landscape filled with Irish icons until he falls in a boiling pot of gold. At this point, he wakes up to find himself in a puddle of water still standing where he fell after being hit by the mace. Panicked and disoriented, he runs away from the castle. O'Toole watches him run, shaking hands with himself (actually O'Pat, the other leprechaun) with a mischievous smile.
The title refers to The Wearing of the Green, an old Irish ballad, while the green shoes themselves are borrowed from the Hans Christian Anderson fable The Red Shoes (and the 1948 film based on it) about a pair of ballet shoes that never let their wearer stop dancing. The title was parodied, also as "The Wearing of the Grin," in the Bugs Bunny cartoon What's Up Doc?, where Bugs reveals that being in the play's chorus was his first gig as an "actor."
The Wearing of the Grin is a Looney Tunes cartoon directed by Chuck Jones and written by Michael Maltese where Porky Pig spends a night in a castle inhabited by leprechauns. It was released theatrically on July 28, 1951.