His first assignment was as the associate pastor of the Cathedral of the Risen Christ Parish and as a teacher at Pius X High School in Lincoln.

From 1982 to 1985, Jackels was assigned as associate pastor of St. Thomas Aquinas Parish on the campus of the University of Nebraska in Lincoln.

In addition to his teaching duties at Pius X High School, he also served as the assistant vocations director for the diocese during this period.

Jackels returned to Rome in 1997 to work for the Congregation for the Doctrine of the Faith under then Cardinal Joseph Ratzinger, the future Pope Benedict XVI.

[5] He was installed by Archbishop Carlo Vigano, apostolic nuncio to the United States, on May 30, 2013, at the Church of the Nativity in Dubuque.

[6][7] Jackels joined the other three Kansas bishops in approving a pastoral letter opposing embryonic stem cell research.

[11][12] Jackels also voted to approve language changes in the mass to bring the English translation into a better accord with the original Latin at the June 2006 meetings of the USCCB in Los Angeles.