Mosier started his career in the Fauquier County Sheriff's Office. In 1996 he was selected by the State Department to serve in Bosnia and Herzegovina with the International Police Task Force. Following his tenure, he served as the Director of Investigations for the International Justice Mission, focusing on international investigations of human rights violations including human trafficking, violence against women and children, and police abuse of power.[1] He later served as a senior advisor at the Bureau of International Narcotics and Law Enforcement Affairs.[2]
In 2015, Mosier was elected the 60th Sheriff of Fauquier County,[3] and was re-elected in 2019.[4] Governor Ralph Northam appointed Mosier to the Substance Abuse Services Council and the Criminal Justice Service Board in 2020 and 2021, respectively.[5] As Sheriff of Fauquier County, Mosier was named "Best Law Enforcement Officer" by the Warrenton Lifestyle magazine in 2018.[6]
In 2022, Governor Glenn Youngkin nominated Mosier to serve as the 9th Virginia Secretary of Public Safety and Homeland Security, succeeding Brian Moran. During his tenure, he oversaw Virginia's response to the January 2022 North American Blizzard. He was credited by Youngkin as a leader of Virginia's "Operation Bold Blue Line,"[7] a multiagency effort to reduce gun violence and violent crime in Virginia,[8] which the Governor's Office later claimed removed over $31 million worth of illicit narcotics off the street.[9] The initiative was later criticized by the Virginia Democratic Party for not focusing enough on gun safety.[10]
In 2023, Mosier resigned from Youngkin's cabinet and accepted a position at the Loudoun County Sheriff's Office, where he currently serves as Chief Deputy of the Administration & Corrections Bureau.[11][12]
