Boniface was previously an archbishop though without an assigned see, but that ecclesiastical status did not immediately devolve upon the see itself until his successor Lullus; during his reign Mainz became an archdiocese, in 781.

As was generally the case in the Holy Roman Empire, the territory of a prince-bishopric or archbishopric differed from that of the corresponding diocese or archdiocese, which was the purely spiritual jurisdiction of the prince-bishop or archbishop.

In the secularizations that accompanied the Reichsdeputationshauptschluss (German mediatization) of 1803, the seat of the elector, Karl Theodor von Dalberg, was moved to Regensburg, and the electorate lost its left bank territories to France, its right bank areas along the Main below Frankfurt to Hesse-Darmstadt and the Nassau princes, and Eichsfeld and Erfurt to the Kingdom of Prussia.

Dalberg resigned in 1813 and in 1815 the Congress of Vienna divided his territories between the Kingdom of Bavaria, the Electorate of Hesse-Kassel (or Hesse-Cassel), the Grand Duchy of Hesse and the Free City of Frankfurt.

Since then it has had two cardinals and via various concordats was allowed to retain the medieval tradition of the cathedral chapter electing a successor to the bishop.