Niemeyer was born in Princeton, New Jersey. He attended Kenyon College (Artium Baccalaureus, 1962), where he played on the school's baseball team. He then studied at the University of Munich, before pursuing his legal education at Notre Dame Law School (Juris Doctor, 1966). He was admitted to the Maryland bar and practiced commercial law at Piper & Marbury (now DLA Piper) in Baltimore, Maryland, from 1966 to 1988. In 1984, Niemeyer co-authored the "Maryland Rules Commentary", a treatise on the rules of procedure in the Maryland state courts.