Sindy Hooper, 50, finished the race in 16 hours and 24 minutes — the cut-off to finish the race was 17 hours.
Her husband Jon also competed and completed the event.
Hooper swam four kilometres, biked 180 kilometres and ran 42 kilometres, possibly becoming the first person to ever try to race an Ironman while undergoing chemotherapy.
She was diagnosed with pancreatic cancer in January, and underwent surgery to remove half of her pancreas, stomach and gallbladder.
Statistics gave her only a 10 per cent chance to live five more years.
The mother of two competed in the race last year and had signed up to do it again.
Hooper said that last year, she finished in 11 hours and 38 minutes.
Hooper underwent a round of chemotherapy in February and she will undergo the treatment again in September.
She said her doctor called her crazy when she asked him if she could do the Ironman while undergoing chemotherapy.
"He was just looking at me in disbelief, just shaking his head," she told CBC News before heading to Whistler for the race.
"He actually said, 'You know Sindy, I don't understand why a person that's completely healthy would want to do this. I'm not sure how you're going to be able to do it.'"
Hooper has three more races lined up in the coming months.
The winners of the weekend Ironman were Uli Bromme of Colorado (9:28:13) in the women's category, and Trevor Wurtle of Kelowna, B.C., (8:39:33) for the men.