In July 1914, with the support of Jean Jaurès during his candidacy, Moutet was elected Député (Member) in the National Assembly of France representing the Lyon-Vaise district, Rhône.

[6] He became a specialist on questions related to the French colonial empire, advocating a generous policy of assimilation, opposing brutal repression and condescending paternalism.

To improve the plight of colonized peoples, he removed the Indigénat Code of its substance in the years 1936 and 1937, and completely repealed it on 6 April 1938.

[7] On 14 May 1939, at the Congress of the federation of French Section of the Workers' International which met at Drôme, he stated that "every concession (to the Axis Powers) brings us closer to war."

He subsequently went underground and took refuge in Switzerland from 1941 to avoid arrest,[11] with one of his sons being confined to his place in Vals-les-Bains by the Vichy government in retaliation.

He held the Minister of Overseas France position under Félix Gouin, Georges Bidault, Blum's third government, and Paul Ramadier.

He negotiated with Ho Chi Minh and founded Le fonds d'investissement des départements d'outre-mer (FIDOM) (Investment Fund for Economic and Social territories overseas).

From 1947, he was in the French Sudan, and that year he attempted to pass the Code du travail by decree before he left office in November.