She ruled through the First World War, and her perceived support for the German occupation forces led to great unpopularity in Luxembourg as well as neighbouring France and Belgium.

On the advice of Parliament and under enormous pressure from the Luxembourgish people, she abdicated on 14 January 1919 in favour of her younger sister Charlotte, who managed to save the monarchy and the dynasty in a national referendum later that year.

Marie-Adélaïde was born on 14 June 1894 in Berg Castle as the eldest child of Grand Duke William IV and his wife, Marie Anne of Portugal.

Since her father had six daughters and no sons, he proclaimed Marie-Adélaïde as the heiress presumptive on 10 July 1907, in order to solve any succession crisis due to the use of Salic law in the monarchy.

Her mother served as regent until Marie-Adélaïde's eighteenth birthday on 18 June 1912, when the President of the Chamber Auguste Laval swore her in as the first Luxembourgish monarch to be born in the territory since Count John the Blind (1296–1346).

On the day of her ascension to the throne – 25 February 1912 – she refused to sign a new law reducing the role of Roman Catholic priests within the education system.

[3] With the outbreak of World War I, Luxembourg found itself in a dangerous position, unable to defend itself from German invasion because of its neutral status (see Treaty of London (1867)).

When Germany violated Luxembourg's neutrality on August 2, on the pretext of safeguarding the railroads, Marie Adelaide and her government responded with formal protests.

[1] During the war, Marie-Adélaïde, her sisters and their mother were personally involved in the work of the Red Cross in Luxembourg, and cared for both German and French soldiers.

[3] This action was permissible under the Constitution, but regarded as unconventional, and provoked an outcry and long-term resentment among the socialists and liberals in parliament, who saw it as resembling a coup d'état.