The daughter of explorer Montgomery Clyde, a young Millicent dreamed that her father's discoveries would one day make her rich. After stumbling upon a family of remarkable bears in Peru, however, Montgomery was so amazed that he could not bear to let any harm come to them. This decision cost him his title and career, but he did not mind, and instead was content devoting himself to running a petting zoo. Millicent, on the other hand, was appalled.
As an adult, Millicent became a taxidermist for the British Museum; though secretly, she began killing and stuffing animals that have been illegally shipped in from all around the world. One night, she learns that a particular marmalade-loving bear (the film's titular hero) has recently appeared in the area. Knowing immediately that this is one of the bears that drove her father down a path of ethics, Millicent becomes determined to find Paddington and make him the center of her collection.
After a failed attempt to seize him, Millicent is delighted to discover that Paddington has unwittingly come to her in his search for Montgomery, who he learns is now deceased. The taxidermist attempts to kill the bear at the museum, but he is aided by his new loving family, the Browns, who have come looking for him. A showdown takes place on the roof of the building, with Millicent on the far edge of one side, the Browns on the other, and Paddington in the center. His last hope of escape, the bear quickly removes a marmalade sandwich from beneath his hat which had been kept there ever since leaving Peru, and throws it at the woman. A flock of pigeons immediately chase after the launched food item, causing Millicent to stumble backwards, but ultimately, failing to knock her off. That is, until Mrs. Bird opens a hatch from below the villainess's feet. Millicent falls off and is forced to hang on to a pole until the authorities arrive. She is later tried and sentenced to community service at a petting zoo. Her final scene involves a monkey dumping a bulldozer scoop of manure on her as she cleans an animal pen.
- Nicole Kidman previously portrayed the evil Tracy Safian in the 1993 thriller Malice, and later played protagonist villainess Erin Bell in 2018's Destroyer.