[4] During the Schmalkaldic War of 1546/47, the Lower Saxon city became a refuge for Protestant scholars, which earned it the epithet Herrgotts Kanzlei (German for 'Lord's Chancellery'),[5] but also an Imperial ban that lasted until 1562.

[7] The Roman Catholic archdiocese had de facto turned void since 1557, when the last papally confirmed prince-archbishop, the Lutheran Sigismund of Brandenburg, came of age and ascended to the see.

[9] From about 1600, he styled himself Administrator of Magdeburg, as did other Protestant German notables assigned to govern principalities that were de jure property of the Catholic church.

[9] As a result of these developments, in January 1628, the Magdeburg cathedral chapter deposed Christian William and elected Augustus of Wettin, 13-year-old son of John George I, Elector of Saxony, as Administrator.

[13]: 128  The Swedish king was a Lutheran Christian, and many of Magdeburg's residents were convinced that he would aid them in their struggle against the Roman Catholic Habsburg emperor, Ferdinand II.

However, not all Protestant princes of the Holy Roman Empire had immediately embraced Adolphus;[14]: 107  some believed his chief motive for entering the war was to take northern German ports, which would allow him to control commerce in the Baltic Sea.

[13]: 129 [15] In November 1630, King Gustavus sent ex-Administrator Christian William back to Magdeburg, along with Dietrich von Falkenberg to direct the city's military affairs.

[10]: 167 When the Magdeburg citizens refused to pay a tribute demanded by the emperor, Imperial forces under the command of a Flemish mercenary, Johann Tserclaes, Count of Tilly laid siege to the city within a matter of months.

[14]: 107  The city was besieged from 20 March 1631 and Tilly put his subordinate Imperial Field Marshal Gottfried Heinrich Graf zu Pappenheim, a Catholic convert, in command while he campaigned elsewhere.

The fortifications were breached and Imperial forces were able to overpower the defenders to open the Kröcken Gate, which allowed the entire army to enter the city to plunder it.

[14]: 112 Duke Maximilian of Bavaria, president of the Catholic League, concluded a congratulatory letter to Tilly on 1 June with the wish that "the enemies, powers and forces opposing Catholicism, the only religion offering salvation, would finally be ruined.

After the sack, the Archbishopric of Magdeburg went to Archduke Leopold Wilhelm of Austria, youngest son of Emperor Ferdinand II, as the new Catholic administrator.

The Peace of Prague (1635) confirmed his rule over the city, but three years later, Swedish troops expelled the Habsburg army and restored Augustus of Wettin (first elected in 1628) as Administrator as of October 1638.

Augustus finally took full control of Magdeburg in December 1642 after a neutrality treaty was concluded with the Swedish general Lennart Torstenson.