NEW YORK — The head of New York City’s jails stepped down Friday, announcing his retirement earlier than expected after a series of scandals that cast a shadow over his efforts to reform a system plagued by violence and corruption.

Correction Commissioner Joseph Ponte, 70, succumbed to mounting pressure for his ouster three years after Mayor Bill de Blasio gave him a mandate to transform a culture of abuse in the sprawling Rikers Island complex and the city’s other jails.

While critics acknowledge Ponte made progress, recent accusations that his department’s watchdog spied on city inspectors marred his tenure. Ponte also was reprimanded for improperly using his city-issued vehicle for personal travel and spending months away from the city at his Maine home.

De Blasio, who appointed Ponte in 2014, praised his commissioner on Friday, saying he was a champion of reform during his time in New York, the final chapter in a 40-year career in corrections.

“Joe Ponte has spent his life reforming jails,” de Blasio said in a statement. “While much work remains, there is no doubt that our city’s jails are safer, more rehabilitative, and more humane as a result of Commissioner Ponte’s work.”

Before taking charge of New York City’s jails, Ponte served as frontline correctional officer, a prison warden and commissioner in jails and prisons around the country. He was Maine’s corrections commissioner for three years before taking the New York City post.

Ponte was credited with initiating improvements in Maine’s prison system, receiving praise from prisoner advocates for reducing the number of inmates in segregation.

He had planned to retire within the next several months but decided to leave sooner because the scandals had become a distraction, the New York Times reported before the official announcement Friday, citing anonymous sources.

As calls mounted this week for Ponte’s ouster, de Blasio had staunchly defended him, saying the commissioner acknowledged ethical mistakes and was making restitution.

De Blasio appointed Ponte after making a campaign promise to reform Rikers Island jail, one of the three largest prison complexes in the United States by population.

Ponte tripled the number of surveillance cameras at Rikers and organized training for officers to defuse tense situations.

During his tenure, a number of Rikers Island correctional officers were prosecuted as authorities sought to stem the violence at the complex, which sits on an island in the East River between Queens and the Bronx.

In March, de Blasio declared the city would close Rikers in as little as 10 years, citing falling crime levels that he said portend a long-term trend.