Carly Miller is a young, accomplished woman who is introduced as the new girlfriend of Sam Witwicky in the events of the film. She is characterized as being smart, confident, and savvy, possessing an adept calm that helps her handle even life-threatening situations with a level head. She first met Sam Witwicky at the White House under circumstances that are later elaborated upon in supplemental material, where she demonstrated her resourcefulness by using a weapon from a fallen Transformer to save Sam from a Decepticon during a battle at a career fair.

In her day-to-day life, Carly works managing a collection of exotic cars for her boss, the wealthy and charismatic CEO Dylan Gould. Sam is initially insecure about Carly's close working relationship with Dylan, feeling threatened by his money, power, and good looks, but Carly reassures him that Sam has no reason to feel threatened and that her job simply pays for their rent and food. Her primary motivation throughout the story is her love for Sam and her desire for his safety and happiness. She is frustrated with his need to be a hero, believing that he does not know who he is without the danger, and simply wants him to understand that he matters to her above all else.

Carly's role in the story is initially that of Sam's supportive girlfriend, but she becomes a central figure in the final act when she is captured by her boss Dylan, who is secretly a human collaborator with the Decepticons. Dylan uses her as leverage to force Sam to spy on the Autobots, and he brings her to Chicago to witness the Decepticons' plan to bring Cybertron to Earth. Her key relationships include her romantic partnership with Sam, her professional but exploitative connection to the treacherous Dylan Gould, and a friendly bond with Sam's Autobot partner, Bumblebee, who expresses his approval of their relationship by playing wedding chimes with his radio.

Carly demonstrates significant development from a civilian caught in extraordinary events to a direct, active participant in the conflict. While held captive in Chicago, she does not simply wait to be rescued. Instead, she engages in a psychological confrontation with Megatron himself. Approaching the Decepticon leader, she uses manipulation and reverse psychology to play on his ego, suggesting that his ally Sentinel Prime has all the power and that Megatron will be nothing but his subordinate. This clever tactic successfully enrages Megatron, distracting him and drawing him into a vulnerable position that allows Optimus Prime to launch a surprise attack and kill him. This act demonstrates her notable ability to remain composed under extreme pressure and use her wit to influence powerful beings far beyond her physical capabilities.

Among her other notable abilities, Carly is a capable and resourceful individual who is not easily frightened. She maintains a sharp, sarcastic sense of humor even in tense situations, such as when she teasingly calls Sam's jealous temper tantrums sexy. Her bravery and quick thinking, culminating in her direct manipulation of Megatron, prove her to be a decisive factor in the final battle, saving the Autobot leader and helping to turn the tide of the war.