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.
[10][14] Ackermann was formerly the chairperson of the board of governors of Pretoria Boys High School and he was later the South African secretary of the Rhodes Trust from 1988 to 2003.