Scat Cat was originally written for Louis Armstrong to voice him and was originally named Satchmo Cat. Unfortunately for Armstrong, he became ill and was unable to voice the character, leading to the decision to replace him with Scatman Crothers, rename him "Scat Cat" and write a new song, "Everybody Wants to Be a Cat."
One night, Thomas O'Malley brings Duchess and her three tired kittens to his penthouse, where he takes them all in with care and gives them a place to sleep. Jazz music can be heard from inside, and Scat Cat and his Alley Cats are introduced. While playing their instruments, Scat Cat and the gang all sing "Everybody Wants to Be a Cat". O'Malley and Duchess join in the fun, as do Berlioz, Marie and Toulouse. During the song, O'Malley and Duchess perform a dance number, and Duchess sings a wonderful solo while playing the harp; which Scat Cat and the gang find so beautiful, soft, lovely, and romantic until they get back to playing their instruments (with the help of Scat Cat's trumpeting) and make their way out of the penthouse along with other alley cats.
Later, Scat Cat and the gang, upon being informed by O'Malley via Roquefort (the latter of whom nearly got killed by them due to getting the name wrong), come to rescue Duchess and her kittens from Edgar, a greedy butler who is "catnapping" the cats so as to inherit a great fortune. As Scat Cat and the alley cats rush to save Duchess and her kittens, they were also witnessed by a Frenchman about to drink wine. He saw cats seemingly being chased by a mouse (Roquefort), causing the Frenchman to pour his wine onto the ground, implying that he's deeply considering to give up drinking alcohol. After Scat Cat and the gang defeat Edgar, Scat Cat along with the other alley cats get adopted by Madame Bonfamille at the end of the movie.
In the show, Scat Cat, O'Malley, and the other alley cats were all a part of the popular band "O'Malley and the Alley Cats." However, as a running gag in the show, something or someone would prevent the band from playing.