Shannon was born and raised in San Antonio, Texas. As a child Shannon did not dream of being an actress, she had ambitions of competing in cross-country in the Olympics. Unfortunately a knee injury prohibited Shannon from becoming a cross-country track runner. Shannon then became active in theater in high school and, on advice from her high-school acting coach, moved to California to study at the University of Southern California School of Theater. She got her big break when she landed the role of Lindsay Gardner on The O.C.. In 2007 she had her first lead role on the big screen in Graduation and 2008 will see her starring in the feature film Autopilot.