Chief Sullivan began his law enforcement career in Louisville, Kentucky as a member of the Louisville Metro Police Department (LMPD). After more than two decades of numerous assignments, he rose through the ranks and was appointed the Deputy Chief/Chief of Staff (second in command) of the agency in 2015.

In June 2019, Chief Sullivan was recruited by the Baltimore Police Department (BPD) to serve as Deputy Commissioner of the Operations Bureau, commanding the Patrol Operations Division, Criminal Investigation Division, and the Data Driven Strategies Division, encompassing over 2,500 sworn and professional members. In 2020, he successfully led BPD's response to the COVID-19 pandemic and oversaw the agency's nationally recognized deployment response to mass demonstrations, protesting the murder of George Floyd. Sullivan also successfully redesigned the agency's COMSTAT process to include an emphasis on total command performance, which led to a reduction in overtime spending while the City experienced a reduction in overall Part I crime.

In June 2021, he took command of BPD's Compliance Bureau directing the BPD Education and Training Academy, Information Technology Division, Consent Decree Implementation Unit, Communications and Records Management Division, Equity Office, and the Performance Standards Section. He worked in collaboration with the community, all Bureaus of the BPD, the Department of Justice Civil Rights Division, the Court Monitoring Team and the Federal Court to advance police reform required by Baltimore's Federal Consent Decree.  The 2022 monitoring report outlined the significant progress the agency made, moving the reform effort from the policy development and training phases, into implementation and assessment of compliance.

Chief Sullivan is a graduate of the Southern Police Institute's Administrative Officers Course, the Federal Bureau of Investigation National Academy, the International Association of Chiefs of Police (IACP)/MacArthur Foundation Institute on Juvenile Justice at Yale University, and the Major Cities Chiefs Association Police Executive Leadership Institute.

In 2018, the Police Executive Research Forum awarded him with the prestigious Gary P. Hayes Award, which recognizes national leaders in the policing profession. He currently serves on the IACP Human and Civil Rights Committee.

Chief Sullivan holds a bachelor's degree in police administration and a master's degree in the administration of justice from the University of Louisville.

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