In 1919, together with Charles de Broqueville and Emile Vandervelde he introduced universal suffrage for all men (one man, one vote) and compulsory education.

As foreign minister during the Great War, Hymans was successful in securing promises from the Allies that amounted to co-belligerency.

Britain, France and Russia pledged in the Declaration of Sainte-Adresse in February 1916 that Belgium would be included in the peace negotiations, its independence would be restored and it would receive monetary compensation from Germany for the damage.

When the war began, Hymans also received major promises of relief support from the United States that were approved by President Woodrow Wilson.

At the Paris Peace Conference in 1919, Belgium officially ended its longtime neutral status and became the first in line to receive reparations payments from Germany.