He started his career as a teacher of Afrikaans, German and history in Randfontein and then attended the University of the Witwatersrand, where he received his PhD.

He was elected mayor for a second term in 1957 and he was a member of the United Municipal Executive of South Africa for four years.

In September 1972, Mulder appointed Eschel Rhoodie as the Secretary of Information and the department began to push propaganda, ultimately spending millions to influence media outlets in South Africa and abroad to support the government's Apartheid policies.

[4] They assisted John McGoff, an American newspaper publisher who supported the administration, in his efforts to purchase The Washington Star and The Sacramento Union.

[4] Though the scandal eventually brought about Vorster's downfall and complete retirement from politics, Mulder lost the ballot to succeed him in September 1978.

From documents that reached The Spectator, in a separate scandal, Mulder had a financial interest in certain South African companies which run a group of private enterprise mental homes for the blacks.

After the 2009 general election, both sons served in the National Assembly of South Africa as Members of Parliament for the Freedom Front Plus.