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,[1] which has grown to become a 40-member regional law firm with offices in Wilkes-Barre and Hazleton, Pennsylvania.
[2] On September 3, 1970, Rosenn was nominated by President Richard Nixon to a seat on the United States Court of Appeals for the Third Circuit vacated by Judge David Henry Stahl.
Rosenn was confirmed by the United States Senate on October 6, 1970, and received his commission the following day.