Julian McMahon was the second of three children born to Sir William and Lady Sonia McMahon. The late Sir William was the former Prime Minister of Australia. Julian studied law at the University of Sydney, but he became bored after one year and began a career in modeling, working primarily in commercials. In 1987, he headed began print modeling assignments in Los Angeles, New York, Milan, Rome and Paris. His appearance in a TV commercial promoting jeans in his home country made him popular enough to be cast as the lead in The Power, the Passion, an Australian "Dynasty"-like series. After 18 months on the series, he starred in Home and Away, another successful series, where he won a best actor award from a national magazine.

McMahon later performed on stage, appearing in a musical version of "Home and Away" in Britain as well as in "Love Letters" in Sydney and Melbourne. After a lead role in the feature film Wet and Wild Summer! with Elliott Gould, he went to Hollywood to read for American projects. In 1992, he was cast as Ian Rain on NBC's daytime drama Another World. After two years, he left to appear in several plays in Los Angeles. He also appeared in the feature film Magenta before landing a role on Profiler.

In his free time, McMahon enjoys surfing, biking, and cooking. He is a fan of baseball, football and basketball, and he collects classic books.
Was once quoted in an Australian magazine article as saying that acting was just another job to bring in money. Has a daughter, Madison (b. June 2000), with Brooke Burns. Has an older sister Melinda and a younger sister Deborah Former son-in-law of Carol Minogue. Former brother-in-law of singer/actress Kylie Minogue and Brendan Minogue. Is fluent in Spanish (as in Nip/Tuck pilot). His surname is pronounced "mic-man". Favorite song is "People are Strange" by The Doors. His character, Cole Turner, was killed off in the landmark 100th episode of Charmed. Attended Sydney Grammar School, a private school in Sydney. Later attended the University of Sydney. Was being considered to take over the role of James Bond from Pierce Brosnan but lost out to Daniel Craig. Was listed as a potential nominee on the 2006 Razzie Award nominating ballot. He was suggested in the Worst Supporting Actor category for his performance in the film Fantastic Four, he failed to receive a nomination however. Is a militant non-smoker. Former brother in law of Brendan Minogue. Former son-in-law of Carol Minogue.