Maulsby practiced law in
Frederick and
Westminster. He was the first state's attorney from Carroll County; serving from 1844 to 1846. Maulsby was president of the
Chesapeake and Ohio Canal from 1857 to 1859. He was a presidential elector for
Stephen A. Douglas in 1860. He served as colonel of the
United States Army's
1st Maryland Infantry Regiment, Potomac Home Brigade during the Civil War. He participated in the battles of Charlestown, Harper's Ferry, Martinsburg, Monacy and Gettysburg. He was a delegate from
Frederick County for the
Maryland Constitution of 1867. Maulsby was appointed chief judge of the 6th judicial circuit court by Governor
Oden Bowie in 1870. He was judge of the Maryland Court of Appeals, then the highest court in the state, from January 20, 1870, to November 7, 1871. He was succeeded by
Richard Bowie. In 1873, he defended Joseph W. Davis, who was accused of murdering his wife. After defending Davis and later learning of his guilt after Davis's confession, he sent his legal fees to the wife of the murder victim and stopped practicing criminal law. ==Personal life==