Brown was brought up as a Methodist but became a Humanist when he met his second wife Diana. He became a life member of the British Humanist Association, the National Secular Society and the Council for Secular Humanism, but only became active in the Humanist movement after attending the 14th World Humanist Congress in Mumbai in 1999. He became a member of the IHEU Committee for Growth and Development later the same year and chair of the Committee in 2000. He was elected a vice-president of IHEU in 2001, and president in 2003. He served as president until 2006.