Dunleavy began his career in Australia in 1953 as a copy boy for The Daily Mirror, an evening newspaper then owned by Ezra Norton.

Arriving in New York on New Year's Eve, 1966 with 10 dollars in his pocket, he worked as a correspondent for London newspapers. He joined the New York Post as a news reporter after Rupert Murdoch purchased the newspaper in 1977.

Like Gordon Elliott, another Australian television personality, he helped create the US tabloid television market in the 1980s; both were reporters for A Current Affair.

Style

Dunleavy's irreverent shock-jock style was the model for actor Robert Downey, Jr.'s performance as Wayne Gale in Oliver Stone's film Natural Born Killers. Downey spent time with Dunleavy as part of preparing for the role.

Retirement

After a 55-year career, Dunleavy's retirement celebration on 1 October 2008 was attended by 400 colleagues and friends. Those who honored Dunleavy included News Corp. Chairman and Chief Executive Rupert Murdoch, Post Editor-in-Chief Col Allan, Police Commissioner Ray Kelly, Uniformed Firefighters Association President Steve Cassidy and former A Current Affair host Maury Povich, accompanied by his wife, Connie Chung.

"Your dedication to your work, your inspiration to others and loyalty to the paper defies description," Murdoch said as Dunleavy and wife Gloria looked on. "It's exceptional. I've never seen anything like it my whole life."

DuMond controversy

Dunleavy controversially wrote a series of articles in defence of Wayne DuMond, a Vietnam veteran who was convicted of rape in Arkansas in 1984, questioning the justice of DuMond's sentence and conviction. DuMond's sentence was eventually reduced to the point where he was paroled; within a year of his release, he went on to rape and murder two women in Missouri. This Willie Horton-like incident resurfaced as a political issue during the 2008 presidential election, since it was Republican candidate Mike Huckabee who secured DuMond's parole while governor of Arkansas.

In 1977 Dunleavy, in association with three of Elvis Presley's former bodyguards, published the paperback Elvis - What happened? (ISBN 978-0345272157) which investigated Presley's life behind the scenes. It was published on August 1, just two weeks before Presley's death on August 16. This was the first book that focused on Presley's addiction to prescription drugs. Following Presley's death in August 1977, the book sold more than 1 million copies.