His wife, Kelly Paniagua, confirmed he passed away on Wednesday, 2 July, in Clearwater, Florida, after a private battle with cancer.
McMahon was widely known for his roles as Cole Turner in Charmed and Dr Christian Troy in Nip/Tuck, for which he received a Golden Globe nomination.
The Sydney-born actor, son of a former Australian prime minister, also starred in the Fantastic Four films and his final role was in Netflix's The Residence.
Tributes have been shared by former co-stars including Nicolas Cage, Rose McGowan, and Ioan Gruffudd.