On June 30, 2021, President Joe Biden announced his intent to nominate Sung to serve as a United States circuit judge of the United States Court of Appeals for the Ninth Circuit. On July 13, 2021, her nomination was sent to the Senate. President Biden nominated Sung to the seat to be vacated by Judge Susan P. Graber, who announced her intent to assume senior status upon confirmation of a successor. On September 14, 2021, a hearing on her nomination was held before the Senate Judiciary Committee. During the hearing, Senators questioned her about her decision to sign a letter regarding Brett Kavanaugh's nomination to the U.S. Supreme Court. The letter accused Kavanaugh of being an "intellectually and morally bankrupt ideologue" and claimed that "people will die if he is confirmed". Sung said she recognized that much of the letter's rhetoric "was overheated," but she did not disavow the letter or say "whether she thought Kavanaugh was indeed 'intellectually and morally bankrupt.'" On October 21, 2021, the Senate Judiciary Committee was deadlocked by a 10–10 vote. On November 3, 2021, the United States Senate discharge Sung's nomination from committee by a 49–49 vote, with Vice President Kamala Harris breaking the tie.
