George Claassen studied at the University of Pretoria (B.Hons, MA ) and at (PhD). From 1974 he worked as a journalist at Beeld in various positions as general, political, science and sports reporter. After four years as senior researcher at the Human Sciences Research Council, he joined the Department of Journalism at the Technikon in Pretoria (now the Tshwane University of Technology), where he was Head of the Department from 1989 until 1992. Between October 1993 and the end of January 2001 he was Professor and Head of the postgraduate Department of Journalism at Stellenbosch University in the Western Cape.Here he established the first course in science and technology journalism at an African university.
Until August 2006, he was the Science editor at the Afrikaans daily paper Die Burger, published in Cape Town, where he wrote the controversial weekly column "Wetenskap vandag" (Science Today). Claassen is known for his anti-Intelligent Design opinions and is often criticized by religious groups as being biased in his articles published in Die Burger. In August 2006, there were renewed criticism over his controversial review of "Die Groot Avontuur: Wondere Van Die Lewe Op Aarde", by Leon Rousseau.
The review sparked an intense debate in Afrikaans newspapers, and specifically Die Burger. In his review he criticized the eminent evolutionary scientist, Prof. Phillip Tobias, for writing an "Avant Propos" for Rousseau's book. Claassen's main criticism against Rousseau's book was that it tried to present the development of life on Earth through the eyes of Intelligent Design. Tobias later recanted and distanced himself unequivocally from the Intelligent Design parts of the book in a letter published in Die Burger.
Claassen's latest book, "Geloof, Bygeloof en Ander Wensdenkery - Perspektiewe oor Ontdekkings en Irrasionaliteite" was published by Protea Boekhuis in July 2007. It became an immediate bestseller and in February 2008 went into a 2nd printing. As the founder director of Sceptic South Africa (SSA), Claassen wrote a popular and very controversial blog on science and rational thinking. He deleted his blog: Prometheus Ongebonde, in 2009, without any explanation. It was rumored that he and his family had been personally targeted by fundamental Christians because he was questioning religion in the public schools.
In 2003 Claassen became the ombudsman of the Afrikaans daily newspaper published in Cape Town and Port Elizabeth, Die Burger and served as a board member of the international Organisation of Newsombudsmen.
In May 2007 Claassen was the first winner of the SAASTA South African Science Communicator of the Year Award, presented by the National Science and Technology Forum. In July 2008, Claassen left the newspaper, now following a career as science journalist. He still teaches science journalism at Stellenbosch University, and presents an annual course in Science Communication to scientists at the University of Cape Town. He is writing a book on the Afrikaans press and the role it played during the years of apartheid.