He was active in legislation related to agriculture and was the driving force behind introduction of the Appellation d'origine contrôlée for French wines.

He was appointed Minister of Agriculture on 29 March 1924 in the third cabinet of Raymond Poincaré, He was reelected deputy for the Gironde in the general elections of 11 May 1924 on the Republican Concentration platform.

On 3 January 1926 Capus and Paul founded the wine-making syndicate of Graves and Vayres to combine the winegrowers of this Bordeaux wine region in order to protect them against competition.

[1] During World War II (1939–45), on 10 July 1940 he voted to give Marshal Philippe Pétain the power to form a new government in Vichy.

[4] In 1906 Capus spoke at a congress of the Société des Viticulteurs de France in which attendees tried to describe the distinctive qualities of the wines from their regions.

Capus represented growers of the Gironde, and when he spoke made the case for adding "controllée" (controlled) to "appellation d'origine".

To confirm a wine's origin the authorities would have to taste it and analyze the chemical composition, and for this to work there had to be standards defining the types of grape used, yield, purity and content of alcohol.

[5] Some years later, Pierre Le Roy de Boiseaumarié insisted on tighter regulations in Châteauneuf-du-Pape, and Capus then worked to ensure that quality controls for the appellations were introduced throughout France.

[6] The legislation required that vinters follow "best practices" in growing grapes and making wine, with the civil courts ruling in case of disputes.

[7] Under this law the Comité National des appellations d'origine (CNAO) was given the sole authority to rule on matters related to the quality of wine.

Many small wine producers were eager to escape the state regulations imposed on bulk winemakers, and sought to join.