Mathew wrote poetry, drama, radio plays and filmscripts, short stories, novels, arts and literature criticism, and other non-fiction.
During the 1950s Mathew also worked in shops, moved furniture, gave school broadcasts and adult education lectures, wrote literary reviews for the Sydney Morning Herald as a freelance journalist, worked for the CSIRO as an accounts officer 1952–1954 and was a tutor and lecturer at the University of Sydney 1955–1960.
After some time there he moved to London, where he lived until 1968 when he went to New York and met the inventor, Paul Kollsman and his wife Eva.
In 1969, he wrote in a letter to his Australian artist friend, Pixie O'Harris, "I have probably not been happier in my life.
She donated his papers to the National Library of Australia following his death and established a trust to support research into Australian writers.