[2] In 1843, he became secretary to Bishop Peter Joseph Blum [de], who was only ten years his senior.
[1] In 1867, Klein entered the Prussian House of Representatives as a member of the Centre Party for the Lower Westerwald district.
[1] In 1876, Bishop Blum was no longer accepted by the Prussian government; threatened by disciplinary actions, he fled to Bohemia.
In 1886, Klein was appointed Bishop of Limburg by Pope Leo XIII as the successor to Christian Roos.
[5] During his tenure, several orders founded or reestablished monasteries in the diocese, including the Cistercians, Pallottines and Ursulines.