“There was a point in my life where I literally lived through a camera.”

Cara Delevingne, a confident tangle of lanky limbs and messy hair, tattoos and ripped black jeans, arched her eyebrows and popped her eyes wide as she excitedly described her habit of filming her meteoric, globe-trotting rise. “Watching Lars Ulrich play a Metallica show from behind the drum kit! Or doing tequila shots with Whitney Houston just before she died! When I get older, I’m going to go through that footage and have the best time, because I probably won’t remember much of it.”

For her next adventure, the unfiltered Ms. Delevingne, at 22 the reigning “It” Brit supermodel, is planting her Union Jack in Hollywood with a much-coveted part in “Paper Towns“ (due Friday), the second film based on a novel by John Green, whose “The Fault in Our Stars“ became a $300 million hit worldwide and helped make Shailene Woodley a star.

You don’t have to be one of Ms. Delevingne’s more than 15 million Instagram followers to see why she was a good fit for the role of the rebellious teenager Margo Roth Spiegelman. In “Paper Towns,” the character is described by her neighborhood admirer as “arguably the most gorgeous creature God had ever created,” a girl “whose life is a series of unbelievably epic adventures.” Ms. Delevingne has been a professionally gorgeous model for Burberry and other brands, an angel for Victoria’s Secret, and, most recently, the windswept cover girl of the July issue of Vogue.

But Ms. Delevingne is hardly the only attractive young woman in Hollywood, and she is certainly one of the least experienced. Moreover, in Hollywood, where nearly every lead actor, male or female, is also a fashion model — often making far more money on commercial endorsements than cinema — models are regarded with unease, and often for good reason. Ms. Delevingne understands. She recalls running into the fellow supermodel Rosie Huntington-Whiteley at the Met Ball, shortly after she was cast in “Transformers: Dark of the Moon.”