The 70-year-old said while she had “always enjoyed being active”, she first started competitive running in her 40s.
“I used to play tennis and squash and did mountain walking – then running gradually crept onto the scene,” she told BBC Radio Bristol.
Ms Orme then took her running to the next level, competing in 5km, 10km, and half-marathons, before making the decision to complete a full marathon while on her way home from taking part in the Bath Half.
“I met somebody on the train and I said ‘oh I think I want to try a marathon’,” she said.
“It was just lucky she was a personal trainer and she said ‘I can help you do that’.
“I sort of haven’t looked back from there.”
Ms Orme completed her first marathon in Edinburgh in 2012, aged 58, and has also ran marathons in Chicago, Boston, New York, London and Tokyo.
She has since taken up triathlon as a cross-training technique.
“I never thought that I’d ever end up where I am now,” she said.