Viviane Wembly, a central human character in the narrative, is a professor of English Literature at the University of Oxford. She holds advanced degrees not only in English literature but also in philosophy and history, reflecting a broad and deep academic background. Despite her scholarly expertise, which includes a thorough knowledge of Arthurian legends, she holds a distinctly cynical and dismissive personal view of those very stories, considering them to be fiction.

Her journey begins when she is forcibly recruited into a conflict of cosmic scale. The reclusive Sir Edmund Burton, who has been observing her, orchestrates her abduction by the Autobot Hot Rod, revealing that she is the last living descendant of the mythical figure Merlin. This revelation thrusts her into a partnership with Cade Yeager, who has been identified as the legendary last knight. Initially, their relationship is marked by mutual annoyance and childish insults, but it quickly evolves into a necessary alliance. Her motivation shifts from irritation and a desire to return to her normal life to a committed effort to save the Earth from destruction as the planet Cybertron threatens to collide with it and drain its life force. Only she can retrieve Merlin's staff, the key to stopping the cataclysm, due to her unique lineage.

Throughout the film, Wembly's role is that of the intellectual key to an ancient mystery. She uses her academic knowledge to decipher clues left by her father, leading her and Cade to a sunken Cybertronian ship where the staff is hidden. Her heritage is the biological trigger that reveals the artifact, and she is ultimately the only one who can remove the staff from its resting place in the ignition chamber to save the planet. Her key relationships include her burgeoning partnership and eventual romantic interest in Cade Yeager, her role as the legacy of her distant ancestor Merlin, and her connection to Sir Edmund Burton, who acts as a guide and reveals her destiny. She also shares a functional but initially antagonistic relationship with her Autobot chauffeur, Hot Rod.

Viviane experiences significant character development, transforming from a skeptical academic who dismisses the legends she studies into a courageous heroine who embraces her heritage and actively participates in a high-stakes global conflict. In a moment of decisive bravery, she defies military orders to run back toward danger, determined to complete her mission and use the staff to stop Quintessa's plan. Her notable abilities are primarily intellectual; she is highly educated, observant, and can read ancient Celtic runes. Her most singular ability, however, is biological: as Merlin's last descendant, her DNA is the key that unlocks the location and true form of Merlin's staff, making her indispensable to the Autobots' mission.