Born in New Plymouth on 16 February 1936, he was the son of Stanley Develle Beetham (a carpenter) and his wife Frances Agnes Amy Watts. Beetham attended New Plymouth Boys' High School from 1951 to 1955. He then went on to the Auckland Secondary Teachers College where he eventually acquired a BA (honours) in History and later an MA. He worked as a secondary school teacher and worked in New Plymouth, Taupo and Piopio before lecturing at Hamilton Teachers' College. The Beetham family were Anglican but he instead joined a Presbyterian bible class and prior to training as a teacher he gave serious consideration to entering the ministry.