Shea started his career in law enforcement with his appointment to the New York City Police Academy in late 1990. After graduating in the top 10% of his academy class, he was sworn in as a Patrolman in April 1991 and assigned to the South Bronx. In April 2014, he was appointed Deputy Commissioner of Operations by then Commissioner William Bratton. Prior to this appointment, he had been a chief commanding the Office of the Deputy Commissioner for Operations. He also commanded the 44th and 50th precincts and the Patrol Borough Bronx Anti-Crime Unit. On April 16, 2018, Shea was promoted to Chief of Detectives. As a Deputy Chief in 2013, he quashed an internal investigation into a sergeant with whom he had a mentoring relationship, Juan Duque, and that sergeant's brother, Ruben Duque. Both had defrauded the department of overtime hours and illegally taken patrol cars home. The story didn't become public until 2018. On November 4, 2019, it was publicly announced that Dermot F. Shea would become the 44th Commissioner of the NYPD. As Commissioner of the NYPD, Shea stated in public testimony on June 22nd, 2020 that NYPD officers who had driven into protesters did not use excessive force and said that the officers who were in the vehicle were being "set upon and attacked, and thankfully they were able to get out of that situation with, to my knowledge, no injuries to anyone." He also said in the public testimony that "Our internal affairs bureau investigated this information and preliminarily we have an accounting of that incident where we have officers in a situation where they’re essentially being penned in by protesters.". Contrary to evidence provided by the New York Times, "Police Commissioner Dermot F. Shea has maintained that misconduct during the protests was confined to “isolated cases” and that officers were confronted with violence by protesters."
Sworn in as a Patrolman - 1991 Promoted to Sergeant - 1995 Promoted to Lieutenant - 1999 Promoted to Captain - 2003 Promoted to Deputy Inspector - 2008 Promoted to Inspector - 2010 Promoted to Deputy Chief - 2013 Deputy Commissioner of Operations - 2014 Designated Chief of Crime Control Strategies, January 1, 2017 Promoted to Chief of Detectives - 2018 New York City Police Commissioner - December 1, 2019
