Born in Paarl, Western Cape, South Africa he grew up in a rural farming community in the Northern Cape, one of 4 siblings. His parents Mike and Marguerite Horn had met Moral Re-Armament (MRA) as students in the 1930s and were committed to making a difference in South African society.
Pieter spent a year in the South African Air force and did studies in electronic engineering but before fully completing his course he felt called to give his full-time to the work of MRA/IofC.
He has worked with MRA/IofC since 1966 and served on the Board of this work in South Africa for over 40 years, both as a Board Member, Secretary and later Chairman of the Board. He was involved in theatre in South Africa, USA, Westminster Theatre, UK and Caux, Switzerland as Production Manager as well as Stage Manager.
The main focus of his work since 1976 has been in reconciliation and trust building programmes in South Africa and other parts of Africa.
He was a founding member of the International Council of MRA/IofC and served for six years. In 2007 he, with others, initiated the African Coordination Group that aimed at supporting the work of IofC in Africa and the coordination of programmes. He served on this Group for seven years. During that period he also served as one of the coordinators of the Harambee Leadership Training programmes that operated in Kenya, South Africa, Ghana, Ethiopia, and Nigeria and later supported the training of Peace Mobilisers for their work in South Sudan in 2013.
Pieter is married to Meryl and they have two married daughters and four grandchildren.