Around the world in 622 days

Ultra-marathon runner Tom Denniss dealt with 60-degree Celsius desert heat, snakes and a near-death experience on a run around the world.

Now, he's ready for a cold beer.

Supporters and school children cheered on Dr Denniss as he ran up the steps of the Sydney Opera House on Friday, completing a 26,000 kilometre run in the name of charity.

The whole adventure took 622 days - and Dr Denniss is confident it'll make him the fastest person ever to circumnavigate the globe on foot.

"I've never been a record holder before," he told reporters just after the finish line.

"I think that's worth an extra beer."

An overwhelmed Dr Denniss said he always thought he'd make it, despite a hair-raising incident in the Andes.

"I was there a little bit too early before the snows had melted and the road was snowed in," he said.

"I had to try to get around it and almost fell down a 1000-foot ice cliff."

It wasn't the only time Dr Denniss had to battle nature.

There were "several incidents with snakes" on top of the extreme heat of the US in summer, he added.

"There was one day in the direct sunlight where I had to run in 60-degree temperatures and that's almost impossible to cope with," he said.

"With an ice bucket and towel around my head every kilometre just to cool me down I managed to get through that."

Despite his gruelling feat, the Sydneysider is in no hurry to kick back, and is already planning to join a cycling trip in Victoria in a fortnight.

And his wife Carmel, who spent two years on the road with him, and was by his side at the finish line, is even more keen to get back on the road.

"She enjoyed it so much she wants me to go around again," Dr Denniss joked.

"Do a lap of honour."

The couple have raised more than $53,000 for Oxfam International so far.

A spokesman for the charity said the funds would go towards working with communities in more than 19 countries.

Donations can be made to www.tomsnextstep.com.