Guy La Chambre was born on 5 June 1898, into a prosperous family with roots in Brittany.

In 1916 he enlisted as a volunteer in the French Army and served for the remainder of the First World War, being awarded the Croix de guerre 1914–1918 for his services.

In the aftermath of the German defeat La Chambre served with the Allied occupation forces in the Rhineland.

After completing his legal studies and being admitted to the bar, La Chambre was employed working in the private office of Prime Minister Aristide Briand.

On 10 July 1940, he voted in favour of granting the cabinet presided by Marshal Philippe Pétain authority to draw up a new constitution, thereby effectively ending the French Third Republic and establishing Vichy France.