Mizelle worked for the Gibson Dunn law firm before serving in several positions in the First Trump administration, including in the United States Department of Justice and the White House.[3][4] From 2019 to 2020, he was the acting chief of staff and later general counsel of the United States Department of Homeland Security.[5] During his tenure, Mizelle was involved in developing and defending border security and deportation policies.[6]
Mizelle was hired by the Jones Day law firm in January 2021.[3][4] Later in 2021, he was appointed by Florida governor Ron DeSantis to serve on the 13th circuit court judicial nominating commission.[7]
Mizelle also served as a commissioner on the Florida Elections Commission starting in 2023.[8]
In December 2024, Mizelle was announced by President Donald Trump as the incoming chief of staff to the United States Department of Justice, claiming Mizelle would "help bring accountability, integrity, and Justice back to the DOJ."[6][9] During his tenure at the DOJ, Mizelle was involved in the last-minute settlement of the $14 billion merger challenge between Hewlett Packard Enterprise and Juniper Networks. The settlement was met with criticism from watchdog organizations, members of Congress, and media outlets, who raised concerns about potential irregularities, political influence, and insider dealings.[10][11]
In September 2025, the DOJ announced that Mizelle would depart from the department early the following month.[12][13][14] He officially left the office in October.[15] Upon the announcement, Mizelle told Axios that he intends to continue supporting the Trump administration and focus on identifying left-wing groups he alleges are involved in political violence in the United States.[16]
In October 2025, Mizelle published an op-ed criticizing perceived weaknesses in local prosecution and advocating for stronger federal intervention, writing, "Across the country, George Soros-backed prosecutors have promised reform but delivered chaos. They’ve adopted cashless bail, declined to prosecute repeat offenders, used diversion programs to avoid jail for the violent and abandoned the police."[17]