When he was 12 years old, he entered the Freising Seminary in Munich. But his studies were interrupted when he was drafted into the German anti-aircraft corps during the last months of World War II.
After the war ended, Joseph returned to the seminary and on June 29, 1951, he was ordained a priest.
He was a professor of theology at universities in Bonn, Munster, Tubingen and Regensburg and participated in the Second Vatican Council as adviser to Cardinal Frings of Cologne.
In 1977 Pablo VI asked Joseph to give up the classroom and named him archbishop of Munich. Months later, he became a cardinal. In 1978, he took part in both conclaves that elected Pope John Paul I and Pope John Paul II. John Paul II elected him Prefect of the Congregation for the Doctrine of the Faith and was later named cardinal bishop.
At age 78, he was elected Bishop of Rome by papal conclave on April 19, 2005.