Adelaide was born about September/October 1045, presumably at the Imperial Palace of Goslar, as the first child of King Henry III of Germany (1016–1056) from his second marriage with the French princess Agnes of Poitou (c.1025–1077), a daughter of Duke William V of Aquitaine.

Henry had vainly hoped for a male heir to the throne; unsettled, the royal couple headed for their coronation by Pope Clement II in Rome the following year.

Two years later, Adelaide succeeded her half-sister as Princess-Abbess of Quedlinburg; she was possibly ordained in Goslar Cathedral at Pentecost 1063, witnessing the violent Precedence Dispute.

In Gandersheim, already the appointment of Beatrice in 1043 (at the age of seven) by King Henry III had caused trouble with the canonesses insisting on their autonomy and electoral rights.

Like her half-sister and predecessor, she remained a reliable support of the Salian rule and backed her brother Henry IV throughout the long Investiture Controversy with Pope Gregory VII as well as in the Saxon Rebellion from 1073 onwards.