In his childhood in the depression, McKenzie's poor rural family lived off the land, selling excess produce from their cows, bees and vegetable garden to be self-sufficient.

His first paid job was loading ice cream trucks in Wagga Wagga during the second world war. After the war, he went to technical college in Sydney and worked in an electrical goods factory, where he wrote a bulletin of factory news. He then worked at the Bankstown Observer, the Armidale Express and then the Daily Mirror. He covered almost every topic at the Mirror, including travelling to New Guinea for the search for Michael Rockefeller, Nelson's son, who had set off in a canoe and was never found.

McKenzie left journalism to write novels and probably also worked as an editor at Horwitz Publications. Beginning around 1955, he wrote crime stories as Mike Boone and war stories as Michael Owen. He wrote six to 12 Carter Brown novels while series author Alan Yates was in the US promoting the Signet's reprint series in the late fifties. He then wrote the Kane series for Webster Publications (1958-1959).

In the sixties, McKenzie returned to newspapers. He became an editorial writer and Chief of Staff on The Sunday Telegraph and ran the history page on The Telegraph Mirror. He mentored a generation of young journalists.

In 1964-1965, McKenzie was working in public relations and organised an international tour to Las Vegas, Monte Carlo, London for George Clampett and Keith Jennings after they made a fortune legally manipulating 'one arm bandit' poker machines in New South Wales. The syndicate was banned from NSW clubs and Australian manufacturers changed the machines to remove the flaw. McKenzie later wrote a book about the events, How We Beat the Bandits (Sydney : South West Publishing, 1965).

He was passionate about progressive politics and social justice. While dying from cancer, a nurse asked if he was allergic to anything. "Only John Howard," he said.