Former Massachusetts Governor William Weld is joining Mintz Levin Cohn Ferris Glovsky and Popeo and its government consulting arm. He will be a partner at the Boston-based firm and a principal at its ML Strategies LLC affiliate. His start date is October 22.

Weld, who served as governor of Massachusetts from 1991 to 1997, will be based in Mintz’s Boston offices.

He joins Mintz from McDermott Will & Emery, where he is of counsel to the firm’s Washington office. His McDermott practice includes government strategies, corporate and legislative investigations, litigation and managing high-stakes legal crises.

Weld was a McDermott partner from 1997 to 2001, then rejoined the firm 2006. During his first stint, he was head of the New York office from 2000 to 2001.

From 2001 to 2005, Weld picked up private equity experience at New York private equity firm Leeds Equity Partners, which was then called Leeds, Weld & Co.

“Since leaving public life and establishing a highly successful law practice, [Weld] has continued to play an important role in domestic and international affairs, while building extensive relationships with major companies around the world,” said R. Robert Popeo, Mintz Levin’s chairman, in a press release. Popeo also said that Weld’s experience advising Fortune 100 companies on a range of matters, including corporate compliance and international expansion, would be an asset to Mintz’s clients.

In a written statement, Weld said, “Mintz Levin has long been one of the most forward-thinking, results-oriented law firms in the industry, having led the way in creating a government affairs and consulting affiliate and establishing an international footprint through thoughtful, strategic growth.”

Weld graduated from Harvard College and Harvard Law School. He’s admitted to practice in the Massachusetts, New York and the District of Columbia.

Weld served as the U.S. attorney for the District of Massachusetts in the early 1980s. In the last 1980s he ran the Justice Department’s Criminal Division.

Sheri Qualters can be contacted at squalters@alm.com.