Hsu began his legal career as an associate at O'Melveny & Myers and focused on complex class action litigation. After his clerkship with Judge Denny Chin, Hsu worked as a First Amendment legal fellow at the American Civil Liberties Union, where he worked on challenges to Connecticut's campaign finance law and represented clients in federal district court in matters involving suppression of speech. In 2008, Hsu joined the law firm of Paul, Weiss, Rifkind, Wharton & Garrison, where he continued to work on complex litigation matters in both federal and state courts.
In 2011, Hsu worked as counsel for the United States Senate Committee on the Judiciary and in the office of Ranking Member Patrick Leahy. In 2016, he was elevated to chief counsel for nominations, where he oversaw the judicial and executive branch nominees that appeared before the committee. Hsu served as lead counsel on legislative efforts to amend the Voting Rights Act after key provisions were struck down in Shelby County v. Holder.
In 2017, Hsu was named general counsel to then-Senator Kamala Harris, where he advised her on policy related to campaign finance, gun violence, voting, criminal justice reform, civil rights, law enforcement, and tech policy. In 2019, Hsu served as Harris's deputy chief of staff.
In September 2019, Hsu was named national policy director for Kamala Harris 2020 presidential campaign. In August 2020, Hsu became director of judicial nominations for the Biden–Harris Transition Team, where he advised and developed judicial nominations strategy for the Biden administration.
In November 2022, Hsu announced that he was leaving the Biden-Harris Administration at the end of the year.[5] He left office on January 5, 2023[6] and will join Jenner & Block as a partner in its Government Controversies Practice.[7]
