After the 1929 general election Deckers was appointed as Minister of Defence in the Ruijs de Beerenbrouck III cabinet, taking office on 10 August 1929.

Deckers was selected as party leader and parliamentary leader of the Roman Catholic State Party in the House of Representatives following the election of Josef van Schaik as a Speaker of the House of Representatives, taking office on 11 November 1937.

[citation needed] On 10 May 1940 Nazi Germany invaded the Netherlands and the government fled to London to escape the German occupation.

Deckers also served retroactively as chairman of the Roman Catholic State Party from 1 September 1941 after Timotheus Verschuur was detained in Sachsenhausen concentration camp and later died in captivity on 17 April 1945.

Following the end of World War II Queen Wilhelmina ordered a Recall of Parliament and Deckers remained a member of the House of Representatives, taking office on 20 November 1945.