Connie Laurie caught the black marlin during a fishing charter trip off Cooktown, north of Cairns, over the weekend.
Fishing professionals have called the feat "amazing''.
Mrs Laurie says she has been fishing her whole life but snaring the big marlin, which was later released, is something she will never forget.
"I certainly didn't feel 85 when I was bringing it in, I was too busy concentrating on keeping it on and getting it into the boat," she said.
"I try to stay active and as I said, I've always loved fishing and I want to continue doing it down on the Gold Coast."