Throughout the film, Timothy's primary goal is to make Dumbo rich and famous and, above all, help him rescue his mother. He is very clever and extremely caring for Dumbo. He understands Dumbo is crushed that his mother is away from him and tries not to push him too hard. He also speaks with a New York accent.
Throughout the film, Timothy acts as the much needed protector in Dumbo's life, standing up for the saddened elephant when others attack him on account of his abnormally large ears. Oddly enough, despite his size, Timothy has quite a lot of attitude, and is extremely brave, no matter the foe he's up against. He cares for Dumbo, and truly wants him to succeed in life, save his mother, and prove to the world he's not some abomination. And with the determination that Timothy's famous for, the duo manage to accomplish just that. Not only does he acts as Dumbo's manager and motivator, but his closest friend, and for a while, his only friend.
It should be noted that all of Timothy's actions in the film are clearly driven by his sympathy for Dumbo. After seeing the poor elephant abused and shunned by the other female elephants, Timothy doesn't only stand up for him, but takes the young elephant under his wing and sticks by his side throughout the entire film, not once giving up hope.
In the film, Timothy doesn't appear until after Dumbo's mother is taken away. He is shown eating out of a discarded bag of peanuts, and looking with mild scorn at the other circus elephants while they gossip about Mrs. Jumbo and how she was locked away. They mention that they don't blame her, and that it was all the fault of Dumbo, with "ears only a mother could love." Timothy voices to himself that he finds the ears cute, and watches as Dumbo approaches the other elephants, and is given the cold shoulder. The little elephant walks away sadly, and Timothy, upset by the elephants' cruelty, walks into their midst and effortlessly terrifies them due to being a mouse, mocking and scaring them in the process. Afterwards, he goes to try to cheer Dumbo up, but the little elephant is also scared of him. After a failed attempt to bribe him with a peanut, Timothy earns Dumbo's trust when he says that working together, they may free his mother.
Timothy tells Dumbo in order to get his mother out, he must become a star. He struggles to think of an idea for it, but fails until they hear the nearby ringmaster talking to one of his workers about an idea he has: the "pyramid of pachyderms" act, but he fails to think of a climax. Timothy, seeing an opportunity, goes to the ringmaster while he sleeps and poses as his subconscious, tricking him into make Dumbo his climax by having him jump off a springboard and onto a platform at the top of the pyramid. The Ringmaster awakens, thinking it is his own idea, and does so. When the time comes for Dumbo to go out, Timothy ties up his ears in a bow to prevent him from tripping on them, and when Dumbo shows stage fright, he jabs him with a pin to make him run towards the springboard. On his run, however, the bow comes undone, he trips and flies past the springboard onto the ball that the elephants are balanced on. The elephants lose control and roll wildly around the big top, the guests all fleeing before them, and Timothy watching the events with one eye covered. The ball rolls towards Dumbo, who flees, but trips again. All of the elephants go flying, injuring all of them, and breaking down the big top. Timothy was not harmed and tends Dumbo, while the circus tent is been repaired.
Dumbo is then demoted to a clown and put through a humiliating act. Timothy scrubs him off afterwards and cheers him up by helping him visit his mother. They are happy to see each other, and Timothy looks on with contentment, but the visit does not last long before Timothy must take Dumbo back to the circus grounds. Along the way, he tries to convince a crying Dumbo to pull himself together, telling him that crying would only give him the hiccups. Immediately after saying that, he begins to hiccup, and Timothy leads him to a nearby bucket of water...into which the clowns had dropped a bottle of champagne earlier in the evening. Timothy has Dumbo drink the water, holding his breath before swallowing it, and speaks of how they were going to turn their luck around all the while, stopping only when he sees that the water failed to cure Dumbo's hiccups. Timothy looks at the water curiously, but falls in, emerging drunk several seconds later. The two amuse themselves for a short while as Dumbo blows bubbles, but then begin seeing Pink Elephants. The events of the night are left ambiguous as the Pink Elephants have their parade, but in the morning, elephant and mouse are asleep on a high tree branch, observed by a group of crows.
Timothy is awakened when the leader of the crows, Jim Crow, comes down to find out what they were doing. Timothy struggles with consciousness until Jim calls him "brother rat," taking offense to that immediately. Jim points out that they're in a tree, and Timothy anxiously goes to wake Dumbo. He panics upon realizing that they're so high up, and both of them fall into a pond. The crows fall out of the tree laughing, and Timothy grumpily tells Dumbo to ignore them, and they begin heading back to the circus. Before walking a few steps, Timothy begins to wonder how they got in the tree in the first place, quickly rejecting the options of Dumbo climbing or jumping up. Jim jokingly suggests that they flew up, and Timothy is fast to jump on the idea, telling the surprised elephant that he flew, that his ears were perfect wings. The crows find the idea hysterical, and sing When I See an Elephant Fly. An infuriated Timothy berates them, and tells them Dumbo's story. The crows are moved to tears when they hear it, and Timothy turns his back on them before resuming his path to the circus. He's stopped after a few steps when Jim comes down apologizing to him, and offering to help Dumbo learn to fly. He quietly confides to Timothy that what they need is a little "psychology", and plucks a feather from the youngest crow before handing it to Timothy, telling him to use the magic feather. Timothy understands what he implies, that the feather is a placebo that should help increase Dumbo's confidence and make him fly again.
The crows push Dumbo to the edge of a cliff, where Timothy instructs Dumbo to begin flapping his ears like wings. It seems to do nothing but stir up a cloud of dust, but when it clears, Timothy looks down, and sees that Dumbo actually is flying. The crows laugh with joy as they see that they had succeeded, and they and Timothy share a laugh at how the people at the circus were in for a surprise. Back at the circus, Dumbo is back in his act as a clown, poised at a very high platform. Timothy looks down at the watching crowd, encouraging Dumbo and saying that they were on the threshold of success. He confirms that Dumbo has the magic feather, and then instructs him to jump at his cue. As they fall, Dumbo loses hold of the magic feather, and Timothy panickedly tries to convince him that it was just a gag, and that he had the power to fly without it. He pleads for him to open his ears, and at the last minute, the elephant complies. Ecstatic, Timothy directs and watches as Dumbo shows his skills before the circus, paying back the elephants, clowns, and ringmaster for their treatment towards him. Dumbo's fame skyrockets, and Timothy is later shown to become Dumbo's manager, signing a Hollywood contract for him.
Timothy and Dumbo make an appearance in the opening sequence of the 1950s television series Mickey Mouse Club.
Timothy has recurring appearances on the television series House of Mouse. He appears with Dumbo, the crows, and the Pink Elephants and many other famous Disney characters.
In "Donald wants to Fly", he teaches Donald how to fly like with the "Elephants".
In "Pete's House of Villains", he joins the others in to saying "We want Mickey!".
In the Disney Parks, Timothy is not a meetable character but has many statues. He is also seen in Disneyland along with Dumbo as he flies over the Sleeping Beauty Castle. His voice is also heard greeting guests on the Dumbo the Flying Elephant attraction.
Timothy and Dumbo also represent the Disney Fantasy cruise ship.
Timothy appears at the top of the Dumbo attraction. He originally held a whip but it was later changed into the magic feather.
Timothy is seen in Disney's Hollywood Studios version of Fantasmic. He appears in the Bubble Disney montage. In Jubilation, he can be seen holding what appears to a small whip. He is seen in Dumbo's hat during the Flights of Fantasy Parade.
- Timothy is the second "sidekick character" in the animated features, after Jiminy Cricket.
- It is believed that Timothy is able to communicate with humans, as he managed to convince the ringmaster about Dumbo's stunt.
- Timothy was a character which inspired people to create another mouse character almost like him known as Mouse in Goliath II.
- The animation of Timothy scaring the elephants was recycled for use in Goliath II for the scene with the Mouse scaring the elephant herd.
- While trying to comfort Dumbo, Timothy says, "Lots of people with big ears are famous!" According to animation historian John Canemaker on the 2001 DVD release commentary, the line was recognized by audiences of 1941 as a reference to Clark Gable. The line was also featured in the original theatrical trailer.
- Timothy Mouse is a replacement for Red the robin from the original novel. He was used because elephants are supposed to be afraid of mice.
- No one in the film ever said Timothy's name; it was only shown at the end of the film where it is seen in writing.