The defenses were first proposed by Marshal Joffre. He was opposed by modernists such as Paul Reynaud and Charles de Gaulle who favoured investment in armour and aircraft. Joffre had support from Henri Philippe Pétain, and there were a number of reports and commissions organised by the government. It was André Maginot who finally convinced the government to invest in the scheme. Maginot was another veteran of WW I, who became the French Minister of Veteran Affairs and then Minister of War (1928–1931).

The line was built in a number of phases from 1930 by the STG (Service Technique du Génie) overseen by CORF (Commission d'Organisation des Régions Fortifiées). The main construction was largely completed by 1939, at a cost of around 3 billion French francs.

The line stretched from Switzerland to Luxembourg, although a much lighter extension was extended to the channel sea after 1934. The original line construction did not cover the area chosen by the Germans for their first challenge, which was through the Ardennes in 1940, a plan known as Fall Gelb. The location of this attack, probably because of the Maginot line, was through the Belgian Ardennes forest (sector 4) which is off the map to the left of Maginot line sector 6 (as marked).