Hours after John Kerry submitted his resignation from the US Senate in order to take the top post at the State Department, Gov. Deval Patrick tapped his administration’s former chief of staff to fill out the rest of Kerry’s term. William “Mo” Cowan also served as Patrick’s chief legal counsel.

Cowan, whose appointment was announced yesterday morning, will serve until a June 25 special election to fill the Kerry seat. “I am honored and humbled by this appointment today,” Cowan said in a statement. “I pledge to you and the people of Massachusetts that during this interim period I will work as hard as humanly possible to perform my duties with the needs and aspirations of our state’s citizens foremost in mind.”

The 43-year-old Stoughton resident has worked as an attorney at Mintz Levin and as a special assistant district attorney in the Middlesex County District Attorney’s office.

“Mo Cowan … is one of the most brilliant and intelligent individuals in his field,” UMass Boston Chancellor Keith Motley said in a statement. “He is capable and uniquely positioned to serve the governor and the people of the Commonwealth. We all know that we can move forward in positive way, and trust that he knows how to do the job.”

– REPORTER STAFF