For the decade after graduation from Virginia Tech, where he earned bachelor’s and master’s degrees in civil engineering in 1970 and in 1971, respectively, Quillen was a mine superintendent and chief engineer while creating a startup engineering company with a Virginia Tech classmate. At 31, he became president of Paramont Coal Co. before becoming president of WR Grace’s Eastern Coal Group, managing three different coal companies. In 1994, Quillen became president of six of Pittston Coal Co.’s mines—managing divisions in Virginia, West Virginia, Kentucky and Ohio. The following year, he was promoted to executive vice president of sales and marketing, and president of Pittston Coal Sales for Pittston Coal, a business development role, where he specialized in East Asia markets. In 2002, he helped form Alpha Natural Resources, which has since grown to become one of the largest coal suppliers in the U.S. Ten years later, Quillen formally retired as Alpha chairman.

Quillen currently serves as the rector of Virginia Tech’s Board of Visitors, and is a past member of the college and CEE Advisory Boards. In 2006, he was named Distinguished Alumnus of the College and, in 2011, he was named Virginia Business Person of the Year.