At the end, Blake Johnston was carried on the shoulders of friends up Cronulla beach in south Sydney, describing himself as "pretty cooked".
Johnston began surfing early on Thursday morning in aid of mental health awareness.
His effort has raised some A$335,000 (£185,000; $225,000) for charity.
With spotlights to illuminate a section of Cronulla's surf known as "The Alley", Johnston kept going overnight and had ridden over 700 waves by the end.
The previous record of 30 hours and 11 minutes was held by South African Josh Enslin.
The 40-year-old Johnston, a former pro surfer and distance runner, faced the risk of blindness, infected ears and dehydration, as well as sleep deprivation, hypothermia, shark attack and jellyfish stings.
He emerged briefly from the sea at lunchtime on Friday for a medical check-up, and to receive eye-drops.
Johnston left the beach wearing a black cowboy hat while draped in a thermal blanket.
"I surfed at two in the morning with him, and the lights actually went out so it was pitch black," his brother Ben told the Australian Broadcasting Corporation.
"There were a whole bunch of jellyfish out there, so it was interesting to say the least."
Speaking ahead of his challenge, Johnston said: "I thought, I could just do it. I can run for 40 hours,"
"But, this way, I can surf with people, bring in the community and make a difference for the future."
Johnston is fundraising for the Chumpy Pullin Foundation, set up in the memory of Australian Olympic snowboarder Alex 'Chumpy' Pullin who drowned off the Gold Coast while spearfishing in 2020.
He is also supporting mental health charities, partly in tribute to his father who took his own life a decade ago.
Three of his friends have also died from mental health conditions, according to media reports.