Rieger began his career in the church as parochial vicar in various places, including Marburg-Bauerbach,[2] until he became chaplain in 1781 and then preacher at the court of Landgrave Frederick II in Kassel, and from 1795 on parson.
In 1798, Rieger became canon in Amöneburg, and in 1808 he was appointed Grand Almoner of France by King Jérôme Bonaparte of Westphalia.
[3] On 23 June 1828 Rieger, at age 76, was appointed bishop of the newly established diocese of Fulda.
He was ordained on 21 September 1829 by Johann Baptist von Keller.
[4] During his short tenure as bishop, he acted contrary to the decisions of the Landgraviate of Hesse-Kassel on a number of occasions, including: