Thomas O'Malley comes off as a smooth-talking, streetwise cat who relishes his life of freedom out in the open with no rules and no responsibilities. All of this changes when he meets Duchess for the first time. He falls in love with Duchess when he first meets her, and he quickly starts flirting with and serenading her. Although he was obviously a little turned off by the fact that Duchess has kittens, but he and the kittens quickly grow on each other and he becomes like a father to them. Also, when faced with an adversity, O'Malley will indeed rise to the occasion to protect the ones that he cares for and loves.
In the film, O'Malley appears after Edgar kidnaps and tries to get rid of the cats, but is chased off by a couple of dogs. He is instantly attracted to Duchess because of her appearance, but is slightly put off when he learns she has children. However, he soon has a change of heart and helps Duchess and her children get back to Paris safely. During their return to Paris, he becomes smitten with Duchess once again and starts being fond of her children as well as her. In the big fight scene, he and the Alley cats battle Edgar as he tries to send Duchess and her kittens to Timbuktu. He saves Duchess and the kids and becomes a part of the family.
- “Showbiz. It happens.”
- ―O'Malley after being fired by Mickey again
Thomas O'Malley, along with his alley cat friends, made several appearances on Disney's 2001-2003 television series House of Mouse. As a running gag, he and Scat Cat's group were often booked to sing at the club, but an incident of some sort would always result in them being fired (such as Donald booking the Big Bad Wolf to sing instead) or forced to leave (such as being chased by Pluto). In the episode "Max's Embarrassing Date", O'Malley and Duchess are seen next to a tipped table covered in milk after Goofy has an accident.
Although O'Malley does not appear in this film, Lyle, the cat friend of Dixie, briefly mentions that she has been the girlfriend of "a romeo named Thomas O'…" but before she had time to finish its sentence, Dixie cuts the word to him.
- Thomas O'Malley has become the subject of a popular internet meme about an infamous episode of the UK Gameshow Family Fortunes, in which presenter Max Bygraves asks the question, "Name a famous Irishman." Thomas O'Malley was one of the infamous stupid answers.
- In the Italian dub, O'Malley is known as "Romeo." He's Roman and his most famous sentence is "Io so' Romeo, er mejo der Corosseo" ("I am Romeo, the best of the Colosseum").
- Thomas O'Malley has notable similarities to Tramp.
- Both were stray animals.
- Both fall in love with a house pet. (Lady, Duchess)
- Both roamed wherever they wanted before marrying their love interests.
- Both heroically saved the main characters from time to time.
- Both try to convince their loved ones to stay with them, but fail.
- Both come to their loved ones' rescues in the climax. Tramp goes to save the baby from a rat to Lady's urgings, and Thomas O' Malley saves Duchess and her kittens from being shipped off to Timbuktu.
- Both settle down to become fathers (and on a minor note, also have family photos taken).
- Both have a son who looks like them. Scamp looks similar to Tramp and Toulouse looks similar to Thomas (Although Toulouse was only O'Malley's step-son where Scamp was Tramp's biological child).
Characters: Duchess | Thomas O'Malley | Toulouse | Marie | Berlioz | Roquefort | Frou-Frou | Edgar | Madame Adelaide Bonfamille | Georges Hautecourt | The Milkman | Napoleon and Lafayette | Abigail and Amelia Gabble | Uncle Waldo | Scat Cat | Alley cats | Elvira (deleted)