William "Mo" Cowan was appointed to the United States Senate by Governor Deval L. Patrick on February 1, 2013, to fill the vacancy caused by the resignation of John F. Kerry.

Senator Cowan was born in Yadkinville, North Carolina on April 4, 1969. He graduated from Duke University in 1991 and Northeastern University School of Law in 1994.

Cowan went on to practice as a litigation associate with the Boston firm Peabody and Arnold until 1997, and from 1997 to 2009, he practiced civil litigation as an associate and later as a partner in the Boston office of Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C. During his time there, he represented a diverse array of commercial clients in matters involving corporate governance, financial mismanagement and malfeasance and money laundering investigations, as well as clients at trial on cases involving environmental releases and remediation, patent disputes and consumer protection claims.

 Cowan served for six months in 2000 as a Special Assistant District Attorney in the Office of the Middlesex County District Attorney. He was lead prosecutor in several jury and bench trials in the Framingham District Court.

In 2009, Cowan went on to serve as Governor Deval Patrick's Chief Legal Counsel, advising the governor on legal and policy issues, judicial selection, legislation and all legal issues concerning the governor and the Office of the Governor. In December 2010, Governor Patrick appointed him to serve as his chief of staff.

Cowan has been recognized as an "Outstanding Young Leader" by the Boston Jaycees (2000), a "Corporate Citizen of the Month" by the Boston Bar Journal (July 2001), a "Top 40 Business Leader Under 40" by the Boston Business Journal (2003) and as a "Massachusetts Super Lawyer" (2004 - 2010). He also is a certificate recipient from Harvard Business School for the course "Leading Professional Service Firms".

Cowan is active in his community, serving as a director and officer of several not-for-profit organizations over the years. He serves on the Corporation for Northeastern University, as a trustee for the Discovering Justice Foundation, as a trustee for The Chestnut Hill School and as director and officer for Project STEP, Inc.

Cowan is a member of the Senate Agriculture, Commerce, and Small Business Committees.