Staalman of the left-wing Christian Democratic Party in the second round in the district of Den Helder. He retained his legal position as tax collector, but was given a leave for undetermined time. He was even promoted to inspector of finances in 1921, while on leave. In the 1918 election Oud stood for elections again, and was elected with 5,000 preference votes, mainly from the former district of Den Helder. While MP, Oud also served as secretary of the VDB national board and editor of the De Vrijzinnige Democraat, the party's magazine. In parliament Oud took a particular interest in military matters and education, and served as the party's finance spokesperson. As MP he served as member of the Committee on the Navy between 1923 and 1933 and the Committee on the Army since 1925. He was chairman of the association for the promotion of public education "People's Education" for many years. After the 1933 election, Oud was appointed Minister of Finance in the second cabinet led by Hendrik Colijn. As minister, he was responsible for a large scale operation of budget cuts, during a time of economic crisis. In 1935 he proposed the Bezuigingswet 1935 ("Budget Cut Act 1935"), which involved many budget cuts and financial reorganisations: salaries of civil servants were cut, the old age pensions were financed in a different way and for budgetary reasons, soldiers were to become civil servants after a certain period. Although his proposals lead to a political crisis, they were nonetheless carried by parliament. In the same year, after Henri Marchant left the VDB following a scandal, Oud succeeded him as political leader of the VDB. Oud led the VDB in the 1937 election and returned to the House of Representatives as chair of the parliamentary party. He also served as chair for the committee on government expenditure. In Rotterdam He left the House of Representatives in 1938 to become mayor of Rotterdam. As mayor he also served in the College of Curators of the University of Rotterdam and as chair of the Association of Dutch Municipalities. After he stepped down in 1952 he became honorary chairman of that association. In 1939 he was elected into the States-Provincial of South Holland. In August 1939 he was offered the position of Minister of Finance in the cabinet of Dirk Jan de Geer, but declined. Controversially, Oud did not resign after the German invasion