Previously, he clerked for Supreme Court justice Anthony Kennedy and Judge Arthur Raymond Randolph of the United States Court of Appeals. He also practiced law with Hogan & Hartson in Washington, DC.
From 1999 to 2007, Yoo was a professor at Vanderbilt University Law School. From 2005 to 2007, Yoo directed Vanderbilt's Technology and Entertainment Law Program. During the 2006-07 school year, he was also a visiting professor at the University of Pennsylvania Law School. He accepted an appointment as a full professor of law at Penn beginning in 2007. Yoo also has a secondary appointment at the Annenberg School for Communication at the University of Pennsylvania.