After the 1925 general election, Welter was appointed Minister of Colonial Affairs in the first Colijn cabinet, taking office on 1 October 1925.

Welter semi-retired from active politic and became active in the public sector served on several state commissions and councils on behalf of the government (Cadastre Agency, Statistics Netherlands and the Welter Commission) and as a diplomat and lobbyist for several economic delegations on behalf of the government.

Returning to the Netherlands in 1945, Welter was appointed to the Senate for the newly founded Catholic People's Party.

In March 1946, he was a member of the parliamentary committee of inquiry into the policy of the Dutch East Indies government.

From the beginning of 1947, the Provisional Catholic Committee of Action acted within the KVP against the Indonesian policy of the Roman/Red coalition.