Deng was born in Khartoum in the Sudan. She escaped the Second Sudanese Civil War with her parents and immigrated to San Antonio, Texas. She arrived in San Antonio at age 12, four years later she signed to Trump modelling agency and moved to New York.
She debuted as a runway model in September 2008 for the spring Jeremy Laing, Kai Kuhne, L’Wren Scott, Proenza Schouler, and Zac Posen shows in New York. She was filmed by Jeremy Kost backstage at the Zac Posen show for New York magazine.
She skipped the fashion weeks in Europe in 2008 in order to finish high school in Texas. She appeared in Teen Vogue several times. She has also been photographed by Tibi Clenci. At age eighteen she became well known for having fallen on the runway for Z Spoke by Zac Posen.