Following his tenure at the SEC and a 24-year career in elected and appointed office that included service in the legislative, executive, and judicial branches of the U.S. government, Cox returned to his home in Southern California and the practice of law, which had been his pre-Washington profession. He joined the Boston-based international law firm of Bingham McCutchen LLP as a partner in the firm's Corporate, M&A and Securities practice, resident in its Orange County office, where in 2014 The Best Lawyers in America named him Lawyer of the Year in the Corporate Governance category. He also served as president of Bingham Consulting LLC, the firm's global strategic consulting business. Following the November 2014 combination of Bingham and the Philadelphia-based international law firm of Morgan, Lewis & Bockius, Cox became a partner of Morgan Lewis and president of Morgan Lewis Consulting LLC. Other recent members of Morgan Lewis Consulting include former Arizona Diamondbacks and San Diego Padres owner Jeff Moorad, former National Labor Relations Board chairman Philip Miscimarra, former New Hampshire Governor Steve Merrill, former California Governor and U.S. Senator Pete Wilson, former Clinton White House Cabinet Secretary Thurgood Marshall, Jr., and former U.S. Ambassador to Ukraine and George Bush Presidential Library Executive Director Roman Popadiuk. While at Morgan Lewis, Cox was again named by The Best Lawyers in America as Lawyer of the Year in Orange County, this time in the Corporate Law category for 2016. In February 2020, Cox retired as a partner of Morgan Lewis and as president of Morgan Lewis Consulting, taking the title of counsel at the law firm.