 During that time, Yohn served as an assistant district attorney (1962–1965) and as a member of the Pennsylvania House of Representatives from 1968 to 1980.In 1981 he was elected as a judge on the court of common pleas for Montgomery County, a position he held until 1991.Yohn was nominated by President George H. W. Bush on June 14, 1991, to a seat on the United States District Court for the Eastern District of Pennsylvania vacated by Judge John P. Fullam.