 Born in 1960, son of barrister Paul Sieghart, a human rights lawyer, campaigner, broadcaster and author, and Felicity Ann Sieghart, chairman of the National Association for Gifted Children, magistrate and later managing director of the Aldeburgh Cinema, William is the older brother of Mary Ann Sieghart.He was educated at Eton and St Anne's College, Oxford.In 1986, he founded Forward Publishing with a business partner Neil Mendoza, an independent contract publisher, publishing magazines, children's books and poetry books.