Greene was born in Jacksonville, Florida, and is the daughter of Michele (née Tatum), who works in insurance, and Joe Greene, a U.S. Marine who now owns his own concrete business.She grew up in Middleburg and Jacksonville, and went to University Christian School before transferring to Wolfson High School when she was in tenth grade. She moved to Los Angeles, California, at the age of 17 to pursue an acting career. Greene has an older brother named Joe, who still resides in Jacksonville with their parents.
Greene is good friends with her Twilight co-stars, particularly Kellan Lutz and Jackson Rathbone whom she knew before filming of the series began. Greene has stated the she grew up watching football and is a Florida Gators fan. She was also seen attending a Green Bay Packers game against the New York Giants with Jonas and Jessica Szohr at Lambeau Field in 2010. In 2009, nude self portraits of Greene were leaked onto the internet. Her attorneys threatened to sue various websites that published the pictures.
She initially planned to become a model, but was told that she was not tall enough at 5'5" to be a fashion model and should instead focus on acting in commercials. After taking commercial and acting classes, she fell in love with acting and realized that she preferred it over modeling. Greene graduated from high school early and moved to L.A. to pursue an acting career. Since then, she has appeared as a guest on such television programs, as Punk'd and Crossing Jordan.
Greene's big break came in 2008 when she was cast as Alice Cullen in Twilight, a film based on the novel of the same name by Stephenie Meyer. She reprised her role as Alice in the 2009 sequel to Twilight, The Twilight Saga: New Moon, 2010's The Twilight Saga: Eclipse, 2011's The Twilight Saga: Breaking Dawn - Part 1, 2012's The Twilight Saga: Breaking Dawn - Part 2.
Greene portrayed Michelle Burkham in the drama film Skateland, which premiered at the 2010 Sundance Film Festival.
She reunited with her Twilight co-star Kellan Lutz in the movie A Warrior's Heart and also stars in thriller film, Summer's Blood, as well as the Dark Castle Entertainment production The Apparition, which began filming on February 1, 2010.
Appearing nude in a bodypainted bikini, Greene posed for SoBe advertisements that ran in the 2010 issue of the Sports Illustrated Swimsuit Edition. She received "The Style Icon Award" at Hollywood Life’s Young Hollywood Awards this year. Greene was also presented an award from the PETA foundation for representing Avon and their no testing on animals policy.
Greene presented an award at the 2010 MTV Video Music Awards on September 12, 2010.