Born to a Jewish family in
Plains,
Pennsylvania, Rosenn received a
Bachelor of Arts degree from
Cornell University in 1929 and a
Bachelor of Laws from the
University of Pennsylvania Law School in 1932. Upon completing law school, Rosenn entered private practice in
Wilkes-Barre, Pennsylvania. Rosenn was an assistant district attorney in Wilkes-Barre from 1941 to 1944, and a First Lieutenant in the
United States Army during
World War II from 1944 to 1946 (in the
JAG Corps in the
Philippines). In 1954, Rosenn,
Mitchell Jenkins and Henry Greenwald founded the Wilkes-Barre law firm of Rosenn, Jenkins & Greenwald, which has grown to become a 40-member regional law firm with offices in Wilkes-Barre and
Hazleton, Pennsylvania. He was a Fellow of the
American College of Trial Lawyers. He was the Pennsylvania Secretary of Public Welfare 1966 to 1967. In 1972, when Wilkes-Barre and the entire
Wyoming Valley area was devastated by a flood, he chaired the Flood Recovery Task Force. ==Federal judicial service==