Barrett was born in Bondi, Australia, the son of George and Marguerite Barrett. He left school at 14 to do a few odd jobs before taking on a trade as a butcher around the eastern suburbs of Sydney. He gave up his trade when a hind of beef fell on him and injured his shoulder. While he was on worker's compensation, he completed three writing courses at the WEA (Workers' Educational Association). When his sickness benefits ran out he worked in various jobs, DJ, barman, or went on the dole. His first writing job was gag writing for disc jockeys on Radio 2SM. He also signed on with a casting agent and started acting in commercials and television series and appeared in what he says are 'two classic A-grade clunkers'; the movies Bullamakanka and The Empty Beach.
Les thought that playing minder to Peregrine Normanhurst III sounded like a dead-set snack: Les would keep Peregrine out of trouble. So what if he was on the run from the IRA? They'd never follow him to Australia... But Les quickly finds himself thrust into an adventure that moves at breakneck speed from the corridors of power in Canberra to the grimy tenements of Belfast, to climax in a nerve-shattering, blood-spattered shootout on a survivalist fortress in the Tweed Valley.