In 1480, he was elected coadjutor with the right to succeed as archbishop. This election result was confirmed by Pope Sixtus IV in 1481, despite the Pope's reservations. After Dieter died, Adalbert succeeded him as ruler of the Archbishopric of Mainz on 8 May 1482. Since he was too young to be ordained as bishop, he became administrator. In 1483, he demanded that the city of Erfurt recognize the suzerainty of Mainz over the city. The archbishop's residence, Martinsburg Castle in Mainz, was completed during Adalbert's reign.
Adalbart died in 1484, before he could be ordained as bishop, so he was never archbishop. He is therefore depicted without mitre and pallium.
Adalbert was unmarried. However, he had an illegitimate daughter named Sybilla.