Diederichs was a National Party member of Parliament from 1953 to 1975. He served as Minister of Economic Affairs from 1958 to 1967, as Minister of Mines from 1961 to 1964, and as Minister of Finance from 1967 to 1975. In the latter capacity he became known as "Mr Gold". He served as the first chancellor of the Rand Afrikaans University and ceremonial State President of South Africa from 1975 until his death, after a short illness, of a heart attack on 21 August 1978 in Cape Town.
