In 1945, after the liberation of the Netherlands, he returned to Rotterdam as mayor, although he was also asked to become mayor of Amsterdam, and he was officially re-appointed in 1946. In the same year the VDB merged with the social democratic SDAP and the left-wing Christian CDU to form the Labour Party. Oud was one of the co-founders of this party and served on the party's board between 1946 and 1947. Meanwhile, he served on many government, business, international and civil society committees, he chaired the government committee for municipal finances between 1946 and 1954, he was member of the board of trustees of the banker Staal, he was member of the pension council of the Dutch Reformed Church since 1946 and he served as chair of the International Union of Municipalities and Local Governments between 1948 and 1954.