He first acted as a judge in August 1976, and in October 1980 he was permanently appointed to the bench of the Transvaal Provincial Division of the Supreme Court of South Africa.
[3] In September 1987, he retired from the bench in order to take up an academic appointment at his alma mater, becoming the Harry Oppenheimer Chair in Human Rights Law at Stellenbosch University.
[3] The chair was newly established with an endowment from the Oppenheimer Foundation, and his students included future legal scholar Pierre de Vos.
[4] Ackermann later said that he left the bench when, partly due to the influence of human rights law expert Louis Henkin, he came to endorse a "total rejection of apartheid" and of the sovereignty of the apartheid-era Parliament.
[2] He held his position at Stellenbosch until the end of 1992, and during that time he was a visiting scholar at Columbia University and the Max Planck Institute for Comparative Public Law.
[2] In January 1993, during the negotiations to end apartheid, Ackermann accepted reappointment to the South African Supreme Court, now in the Cape Provincial Division.
[3] In August 1994, Ackermann became one of five judges whom post-apartheid President Nelson Mandela appointed to the inaugural bench of the newly established Constitutional Court of South Africa.
[3][6] Ackermann played a central role in the development of the court's early jurisprudence on dignity and its relationship to equality and non-discrimination doctrine.