McMahon was born in Sydney, Australia, the second of the three children of Billy McMahon, MP and future Australian Prime Minister, and his wife Sonia McMahon, a former 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, a private boys’ school. in 1994 he married Australian singer and actress Dannii Minogue. 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 (1989-1991). Adam Willits, Sharyn Hodgson (who played his on-screen wife, Carly), Mouche Phillips and Justine Clarke also starred.