New York (CNN) New York Police Department Commissioner James O'Neill is resigning from his post atop the country's largest police force and will take a job in the private sector, he said on Monday.

NYPD Chief of Detectives Dermot Shea, who has been on the force for 28 years, will replace O'Neill, Mayor Bill de Blasio said.

O'Neill began his tenure in September 2016. He previously served as NYPD Chief of Department and has worked as a police officer in New York City since 1983, according to his NYPD bio.

His resignation comes just months after O'Neill announced that he was firing Daniel Pantaleo , the officer accused of fatally choking Eric Garner in 2014. The firing was a fraught choice for O'Neill, who said in August that he would probably not be happy with the decision if he were still an officer.