Mariano was born in the city of Lihue on the island of Kauai in Hawaii, but at the age of 4 relocated with her family to California, where she was raised in the city of Mission Viejo with her two older brothers. At the age of 15 she was discovered in Santa Monica, California by a model scout. After graduating from high school, she moved to New York City, where she continued to model and attended Pace University as a full-time student, receiving her degree in Speech Communications with a Media Studies Concentration.
Mariano has appeared in ads for Abercrombie & Fitch, MAC, Armani Exchange, Sephora, Redken, Old Navy, Dereon, Levi's, Pac Sun, and Rock and Republic, as well in catalogs for Victoria's Secret. She graced the April/May 2007 cover for Complex Magazine's 5th Anniversary Issue. She has walked in fashion shows in Miami and New York. Mariano made her Sports Illustrated Swimsuit Edition debut in 2008 and followed up this appearance in 2009.
Mariano's television credits include Jay-Z's comeback music video "Show Me What You Got" and a cameo in the NBC television series Chuck,several commercials for Old Navy, minor roles in Steven Spielberg's "Minority Report" and Hal Hartley's "The Girl From Monday", as well as a reoccurring role in "Rescue Me". In 2009, she appeared in the music video for "Love Again" by experimental fusion music group Clazziquai Project.
She is represented by model agency IMG in London, New York, and Paris.