Michael Anthony Cox, who worked for the Boston Police Department for more than 30 years before leaving for the police chief job in Ann Arbor, Michigan, will return to serve as the city’s top cop, Mayor Michelle Wu said Wednesday.

Cox, 57, faces the task of reforming a police department in a city with public safety unions that are typically resistant to change. He has had an up-close view of past corruption within the department: Fellow police officers beat him in a case of mistaken identity that later became the focus of a 2009 book called “The Fence: A Police Cover-up Along Boston’s Racial Divide.”

Wu was scheduled to formally announce Cox’s appointment Wednesday morning at the Howes Playground on Roxbury’s Moreland Street, steps away from the Winthrop Street home Cox grew up in. Wu introduced him in a virtual roundtable with reporters early Wednesday morning.

A Roxbury native who later moved to Dorchester, he started at BPD in 1989. Cox left Boston for Ann Arbor in 2019 after rising to the position of BPD superintendent and chief of the bureau of professional development, overseeing the police academy.

“Chief Cox brings decades of experience working at every level within our Boston Police Department,” Wu said Wednesday.

“This is a homecoming for me,” an emotional Cox told reporters. He said he plans to bring back a focus on community policing and seek to diversify the department.

Cox has a master of business administration from Boston University, a master of arts in criminal justice from Curry College and a bachelor of science in business management from Providence College.

Cox was one of three finalists for Detroit police chief in 2020.

In 1995, fellow Boston police officers beat Cox while he was in plainclothes, pursuing a murder suspect in Mattapan. He was left with head injuries and kidney damage as the officers, realizing they had a case of mistaken identity, left him behind and sought a cover-up, according to the book “The Fence.” He would later reach a $1.3 million settlement with the city.

“At the time I must admit it was a personal struggle for me because it was a tough time,” Cox said Wednesday. “But the reality is I love public service. I signed onto the job to do public service. And part of my healing process was: What do I want to do with my life? How do I want to give back?”

Interim Suffolk County DA Kevin Hayden called Cox's record "exemplary." "The journey of Michael Cox from being beaten by fellow Boston Police officers to his appointment as Commissioner of the Boston Police Department is emblematic of criminal legal reform," Hayden said. "I’m grateful to have such a strong partner in building a safer, more equitable Boston."

Larry Calderone, head of the Boston Police Patrolmen's Association, in a statement welcomed Cox back to Boston. "As a former member of BPD, Commissioner Michael Cox has a working understanding an intimate knowledge of the changes needed to better the BPD," he said. "As such, we look forward to working with the new Commissioner as he embraces the challenge of uniting, unifying and further professionalizing one of the best and brightest police departments in the nation."

Carol Rose, executive director of the American Civil Liberties Union of Massachusetts, which has clashed with a past police commissioner who called them "paper warriors," said in a statement that improving culture within the department "will not be easy."

"But Boston now has the opportunity to realize transparency, accountability, and public safety for all people," Rose said. "The ACLU remains committed to our efforts to end longstanding racial disparities in policing, demand meaningful oversight and accountability over the police, and transform Boston’s public safety systems so they center justice, equity, and healing."

There were four finalists for Boston police commissioner. A panel led by a former Supreme Judicial Court justice forwarded the names to Wu after a six-month search process. The names of the other finalists have not been released.

Gregory Long has served as acting police commissioner since last year and was not a candidate for the permanent post.

Mayor Marty Walsh, before leaving City Hall to serve as President Joe Biden’s labor secretary, tapped Dennis White to serve as police commissioner. White was placed on leave, and fired by Acting Mayor Kim Janey, after the Boston Globe reported on domestic abuse allegations from decades ago. White is now locked in a legal battle with the city over his firing.

This story was updated with statements from Kevin Hayden and Larry Calderone. It was additionally updated with the ACLU statement.