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

After the election of 1956 Schmelzer was appointed as State Secretary for the Interior in the Cabinet Drees III, taking office on 29 October 1956.

The office of State Secretary for General Affairs was created specially for Schmelzer and was considered as a de facto Deputy Prime Minister.

On 27 February 1965 the Cabinet Marijnen fell and continued to serve in a demissionary capacity and Schmelzer was appointed as formateur.

[3][4] In February 1971 Schmelzer unexpectedly announced that he was stepping down as party leader and that he would not stand for the general election of 1971 but wanted to run for the Senate.

Schmelzer retired after spending 16 years in national politics and became active in the private sector and public sector; he occupied numerous seats as a corporate director and nonprofit director on several boards of directors and supervisory boards (Douwe Egberts, Akzo, Heijmans, Netherlands Atlantic Association and the Institute of International Relations Clingendael) and served on several state commissions and councils on behalf of the government (KPN, Public Pension Funds PFZW and the Cadastre Agency), as well as served as a diplomat and lobbyist for several economic delegations on behalf of the government and the European Economic Community.

Schmelzer, who joined the newly-formed Christian Democratic Appeal (CDA) in 1980, was known for his abilities as a debater and negotiator.