University of Massachusetts at Amherst (Bachelor of Arts, cum laude, 1976). Western New England College (Master of Public Administration magna cum laude, 1985). Suffolk University Law School (Juris Doctor cum laude, 1985).
He previously served as a State Senator for the Norfolk and Plymouth district (1993–2011) and a State Representative for the 1st Norfolk and 3rd Norfolk districts (1977–1993). He is a Democrat and resides in North Quincy, a neighborhood of Quincy, Massachusetts. Morrissey was born in Quincy, Massachusetts on August 2, 1954.
He attended public schools in Quincy. He received a B.A. from the University of Massachusetts Amherst and an M.P.A. from Western New England College. He graduated from Suffolk University Law School in 1985 with a J.D.
He was elected to the Massachusetts House of Representatives, where he represented the 3rd Norfolk district from 1977 to 1979 and the 1st Norfolk district from 1979 to 1993. He was then elected to the Massachusetts Senate, where he represented the Norfolk and Plymouth district from 1993 to 2011. Morrissey's full term as District Attorney started on January 5, 2011.
He was sworn in early on January 2 to succeed William R. Keating, who resigned to take a seat in the United States House of Representatives.
Member of Squantum & Gull Point Yacht Clubs, Savin Hill Yacht Club, Atlantic Neighborhood Association (founding member), k of c, Elks.
Married Joanne M. Ross. Children: Colby Joanna, James Michael.