Judd J. Carhart lived most of his childhood in Amherst, Massachusetts. After service in, and an honorable discharge from, the United States Army, he graduated from the University of Massachusetts in 1971 and from Suffolk University Law School in 1974. He then became an assistant district attorney in Norfolk County, serving in that position from 1974 to 1977 before joining the faculty at Suffolk University Law School, where he directed the student prosecutor program. From 1978 to 1982, he was an assistant United States attorney, a position that he left to practice both civil and criminal law at the law firm of Carhart, Bonistalli and McCarthy in Boston. He subsequently continued his private practice with the firm of Matrord, DiMauro, Liebel, Fitzgerald and Carhart in Springfield until 1988, when he was initially appointed by Governor Michael Dukakis and then elected the district attorney of the Northwestern District.
In 1993, Governor William Weld appointed Justice Carhart an associate justice of the Superior Court, where he sat until his appointment to the Appeals Court. As an attorney, Justice Carhart was a member of the bar of the First Circuit Court of Appeals, the Federal bar, and the Massachusetts bar. He has the unique distinction of having tried multiple first-degree murder cases through to a jury verdict both as a prosecutor and a defense attorney. He is also a longstanding adjunct professor in the Legal Studies Department at the University of Massachusetts. Appointed to the Appeals Court by Governor Deval Patrick, Justice Carhart joined the Court in 2010. He served the Court until he retired on May 3, 2017.