He played a key role in opposing Henry V, Holy Roman Emperor, during the Investiture Controversy, and secured the election of Lothair III rather than Henry V's chosen heir in 1125, causing later Holy Roman Emperors to make concessions in order to maintain hereditary monarchy.

In exchange for supporting the Emperor in his quest to regain the rights to investiture (which Henry received from Pope Paschal II in 1111), he was given the position of Archbishop-Elector of Mainz.

Henry ended up imprisoning Adalbert for three years (1112–1115) without trial after the archbishop refused to hand over control of the imperial castles.

Strong papal campaigning had meanwhile turned much of the German clergy against the Emperor, and Adalbert soon became the leader of the anti-Imperialist bishops.

After Pope Calixtus II gained power in 1119, he made the archbishop a papal legate, following which Henry attacked Mainz.