[1] Yohn graduated from Princeton University with a Bachelor of Arts degree in 1957 and received his Juris Doctor from the Yale Law School in 1960.
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.
[2] 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.
[2] Yohn was assigned to be the Judge during the Vincent Fumo corruption trial in Philadelphia Federal Court in September 2008.