The Senate seat vacated by Massachusetts Sen. John Kerry, who is headed to the State Department, is now occupied.

Massachusetts Gov. Deval Patrick will appoint William “Mo” Cowan as interim U.S. senator on Wednesday, according to a press statement issued by his office. Cowan will remain in this position until Kerry’s successor is chosen. A special election will be held on June 25.

Kerry received overwhelming support from his Senate colleagues on Tuesday for approval as the nation’s top diplomat. In a letter to Patrick, Kerry wrote that he will officially resign his seat in the Senate – after 28 years of service – on Friday, the same day current Secretary Hillary Clinton will leave the post.

Cowan is a former chief of staff and chief legal counsel to Patrick. According to the governor’s office, the soon-to-be interim senator served in Patrick’s administration in 2009.  He practiced civil litigation as an associate and then as a partner in the Boston office of Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, PC., between 1997 and 2009. Cowan was also a special assistant district attorney in the Office of the Middlesex County District Attorney.

Kerry’s interim replacement is a graduate of Duke University and Northeastern University School of Law. Cowan currently resides in Stoughton, Mass., with his wife, Stacy, and their two young sons.

“The people of the Commonwealth have benefited from his wisdom and good judgment during his time in our office, and will again in the Senate,” Patrick said.

Cowan, who has received support from the district attorney and Rep. Dan Winslow, said he is both honored and humbled by this appointment. He promises to work hard and keep the citizens of Massachusetts at the forefront.