Charlotte Mearing serves as the Director of National Intelligence for the United States in Transformers: Dark of the Moon. In this capacity, she assumes oversight of NEST, the multinational military task force that operates alongside the Autobots. Her background is rooted in high-level government bureaucracy, and she is characterized by an overbearing, controlling, and demanding personality. Mearing is a meticulous professional who insists that every operation, decision, and piece of intelligence be filtered through her office. She has a particular disdain for insubordination or anyone attempting to bypass her authority, regardless of their past record of heroism. Notably, she dislikes being addressed as ma'am, a preference that often adds tension to her interactions with military personnel.

Mearing's primary motivation is maintaining national security through absolute control, though she is pragmatic enough to recognize the larger strategic picture when confronted with overwhelming threats. Initially, she is highly skeptical of civilians and outside input. She questions the continued involvement of Sam Witwicky, viewing him as an inexperienced young man rather than a valuable asset, and she threatens him with treason charges for accessing classified information. Her role in the story is that of an antagonist to the human protagonists early on, representing the obstructive and risk-averse nature of official channels. She is responsible for locking down the newly discovered Pillars and for revoking Bumblebee's permission to reside with Sam. When Sentinel Prime betrays the Autobots and attacks the NEST base, Mearing attempts to confront him directly, demonstrating her willingness to stand up to even the most powerful alien beings, though she has to be physically restrained by Colonel Lennox to keep her from harm.

Mearing has several key relationships that define her arc. She shares a tense, adversarial rapport with Sam Witwicky, initially dismissing him but eventually apologizing after realizing she underestimated his insights regarding the Decepticon plot. With her subordinate, Colonel Lennox, she is demanding and exacting, though she relies on him as a primary liaison to the Autobots. Her most unusual relationship is with the eccentric former agent Seymour Simmons, with whom she had a past romantic encounter. Throughout the Chicago crisis, Simmons attempts to rekindle their connection, which visibly annoys her. However, following the defeat of the Decepticons, Simmons kisses her soundly; in a moment that breaks her stern composure, she laughs before returning to form and ordering him arrested.

Throughout the narrative, Mearing undergoes a subtle but clear development. She begins as a rigid bureaucrat more concerned with protocol than trust, but the severity of the Decepticon invasion forces her to adapt. She loses her condescending attitude when confronted with the catastrophe in Chicago and works collaboratively with Morshower and Simmons to gain intelligence on the situation. Her respect for Witwicky grows to the point where she values his on-the-ground reports. While she has no superhuman abilities, Mearing possesses sharp administrative authority and the security clearance to access the "Total Nightmare file," an extreme threat response protocol. She is also noted for her blunt assessment of those under her command, famously referring to the Wreckers as assholes and explaining that they are kept off base because of their behavior.