McMahon was born in Sydney, New South Wales, Australia, the second of the three children of William McMahon (later Sir William), a politician and later Australian Prime Minister, and his wife Sonia McMahon, an occupational therapist and "fashion icon". He has an older sister, Melinda, and a younger sister, Deborah. McMahon has Irish ancestry.

McMahon was educated at Sydney Grammar School, Read more...

In addition to a career as a fashion model, including a jeans commercial for Levi Strauss, McMahon began an acting career on Australian soap Home and Away, playing the soldier Ben Lucini (1990–1991). McMahon was one of several Home and Away cast-members to star in a stage musical about the soap, which toured the UK in 1991. Adam Willits, Sharyn Hodgson (who played his on-screen wife, Carly), Read more...

McMahon has been married and divorced twice, first briefly, to Australian singer and actress Dannii Minogue and subsequently to American actress Brooke Burns, with whom he had a daughter, Madison Elizabeth born June 9, 2000. He was also linked to Shannen Doherty, his co-star from Charmed.

When he made a guest appearance on The View in October 2006, he presented a rug for Rosie O'Donnell as Read more...