The role is a return to the spotlight for the Queensland-born athlete, who's been working to improve Indigenous education outcomes through her Cathy Freeman Foundation for the past decade.
"At the age of 44, I thought you know what? I've got all of this experience and all of these stories, it'd be such a shame not to share," says Freeman, speaking at an event in Brisbane on Friday.
In 1990, Freeman became the first Aboriginal woman to win gold at a Commonwealth Games in Auckland at only 16 years of age, but is best remembered for her heart-stopping gold medal victory in the 400 metres at the Sydney 2000 Olympics.
"You can never prepare for days like that," she says, reflecting on the iconic moment.
"You do the right things, and when you do make wrong moves you make sure you don’t do it again. But certainly for the reaction after a certain level of success, it’s hard to be prepared for that.
"It’s sort of like being a mother for the first time I suppose. No one shows you how to do it, really."
"All I remember was thinking, in the warm up track, just do what you know.
While working with aspiring elite athletes in her current hometown of Melbourne, Freeman says she's most often asked what was going through her head as she awaited the crack of the starting pistol.
"All I remember was thinking, in the warm up track, just do what you know. And it was really just to keep it that simple, because overthinking isn't good," she says.
"If you truly love what you do, you can overcome anything and you tend to use everybody’s goodwill and best wishes to your advantage, and it absolutely feeds your performance.
"It’s great. It’s lovely to make so many people happy."
Queensland Premier Annastacia Palaszczuk describes Freeman as "one of Australia's most celebrated champions".
"Cathy is the ideal person to sell the Commonwealth Games message – not just here to Queensland, not just to Australia, but right across the world," Ms Palaszczuk says.
"She has a strong connection to the Commonwealth Games and understands what Australian athletes will be going through ahead of competing at a major international event on Australian soil.
"She has an iconic status around the world, and her gold medal at Sydney 2000 is regarded as one of the greatest ever Olympic moments."
Other 2018 Commonwealth Games ambassadors include Sally Pearson, Cameron McEvoy, Anna Meares, Laura Geitz and Kurt Fearnley.