Marking the end of an era in local law enforcement, Mayor Martin Walsh on Monday named a black officer, Superintendent-in-Chief William Gross, as the new commissioner of the 2,200-officer Boston Police Department. The appointment, the first for a person of color in the history of the department, will become effective next week when current Commissioner William Evans will retire to take over as executive director of public safety at Boston College.

Walsh talked about Gross at the Monday morning press conference where he announced the appointment. “Chief Gross is a proven leader who is trusted and respected in the community,” he said. “He is an expert in modern law enforcement. He is the right person for the job.”

Gross worked his way up to become the highest-ranking uniformed officer in the department in 2014 when he was promoted to superintendent-in-chief.

“I am a true street cop,” he said. “I started in Dorchester 1985, and before that as a cadet in 1983. [There were] many calls from my mother, worried because of the atmosphere at the time betwixt the community and BPD. But if you want change, be the change. That’s why I became a police officer.”

Evans, 59, a South Boston native who has been on the force since 1982, served in the commissioner’s role for the last five years, first on an interim basis when he succeeded Ed Davis in 2013. Walsh appointed him to the permanent position in January 2014.

Walsh has been a close friend and dedicated boss, Evans said, referencing multiple daily phone calls between them. “He left me alone and I ran the department I wanted,” Evans said. “There hasn’t been a time throughout my entire career where I didn’t want to go to work.”

An avid runner, Evans said this was the time for him to make a choice that would allow him to spend more time with his family. His wife has patiently waited out his decades on the force, Evans said, smiling.

“We’ve had some really tough obstacles over the last couple years with the environment we’ve been operating in,” Evans said in commending his force, “whether it’s Occupy Boston, the Marathon bombing, Black Lives Matter, Charlottesville. And they’ve shown this city proud.”

While applauding Evans’s work in the post, city and state leaders also welcomed the new forthcoming police commissioner. Suffolk District Attorney Dan Conley said of Evans in a statement: “His unassuming demeanor masks a leader who was fiercely committed to leading a department that would embody the highest standards of professionalism, integrity and innovation and it made him one of the very best partners we as prosecutors could ask for. It has been my privilege and blessing to work with Bill Evans. I’m sorry to see him go, but he leaves the Boston Police Department in very good hands with Commissioner Gross.“

The Massachusetts Association of Minority Law Enforcement Officers (MAMLEO) released a statement saying it was “delighted” by the appointment of Gross and wishing Evans well at Boston College. “It is a monumental moment in time,” the group said. “We pray that moving forward, Commissioner Gross will work with our membership towards transparency in our ranks in order to deliver the best possible police services to the public.”

MAMLEO has doggedly pushed for increased diversity in the Boston Police force, earlier this year joining with other civil rights advocacy groups to call for an investigation into police and fire department hiring practices they say illegally disadvantage applicants of color.

In a statement following the announcement, City Council President Andrea Campbell thanked Evans for “his decades of service to the City of Boston, his commitment to strong community policing strategies, and his partnership over the last few years while I’ve served on the Council, including implementing the body camera pilot program and expanding the police cadet program.”

Campbell, an African-American who represents the diverse District 4 as councillor and sits on the public safety committee, also noted the significance of the first black Boston police commissioner. “I look forward to working in partnership with Commissioner Gross on issues of public safety in my district and across the city, including to increase diversity in our law enforcement ranks,” she said.

Gross, 54, is taking over a force lauded by President Barack Obama during his tenure as a model of community policing, and also one on the cusp of deciding how to fully implement a body camera program for its officers. Segun Idowu, who co-founded the Boston Police Cam Action Team and is running for the 14th Suffolk state representative seat, said Evans displayed “leadership and courage” on the body camera topic.

In a tweet, he also congratulated Gross, saying, “I’m looking forward to continuing my work with him on the urgent issues facing us like the permanent body cam program and youth violence. I know Commissioner Gross will do us proud.”

Addressing his plans as commissioner at the news conference, Gross highlighted the department’s continued commitment to community policing. “Under training, reviewing policy, procedures and practices, we are going to continue to move our department forward. The strategy is to work collaboratively with our village. The strategy is to go forward together.”

The news that Evans was planning to leave his post this summer was first reported by WBZ last month, then initially denied by Evans and Mayor Martin Walsh, who seemed piqued at criticism about the denials on Monday. Walsh doubled down on his objection to WBZ’s use of unnamed sources at the time. “They were not correct,” the mayor. “There was no finalization in the contract department with Boston College and the commissioner, and the unnamed sources weren’t correct, and so I knew those unnamed sources were wrong.”

Chris Triunfo of the State House News Service contributed to this story.