Joseph F. Bruno, the commissioner of New York City’s Office of Emergency Management for a decade, has resigned, after remaining in office for several months at the request of Mayor Bill de Blasio’s aides.

Mr. Bruno, 70, who began working in city government more than four decades ago under Mayor John V. Lindsay, was appointed to his emergency management post in 2004 by Mayor Michael R. Bloomberg. He played a crucial role in managing the city’s preparations and response to Hurricane Sandy in 2012. He has also been a judge and the city’s fire commissioner.

In his resignation letter to Mr. de Blasio, dated June 6, Mr. Bruno noted that he had stayed on in January at the request of the new mayor’s deputies, on the chance “that you and your team would be faced with significant emergencies as you took office.”

The letter continues, “I am sure that neither you nor any of us could have predicted the many significant snowstorms” that affected the city this year.