McMahon won recognition for his roles in television dramas, in portrayals of Ben Lucini in the Australian soap opera Home and Away (1989–91), as Cole Turner in the American supernatural drama Charmed (2000–03), and Christian Troy in the American medical drama Nip/Tuck (2003–10). He also appeared in films with leading and supporting roles, such as Chasing Sleep (2000) alongside Jeff Daniels, Doctor Doom in the Fantastic Four franchise (2005 and 2007), Premonition (2007) starring alongside Sandra Bullock, Red (2010) alongside Bruce Willis, and Bait (2012) alongside Dan Wyllie and Xavier Samuel. McMahon's work in television, particularly with Nip/Tuck, garnered him more success. The series won an Emmy Award and a Golden Globe Award. McMahon played the lead role in Nip/Tuck, alongside Dylan Walsh throughout the entire series' run.