The proud Indigenous woman won the nation's heart when she claimed the gold medal in the womens' 400m race at the 2000 Sydney Olympics.

And weeks out from the October 14 referendum she has used her platform to call on Australians to "open our hearts and change our future".

"I can't remember a time when change has felt so urgent, where momentum has been so strong," she said.

"We have the chance to be part of a moment that brings people together, to work hard for something that we can all believe in and right now each of us can be part of something that really matters."

In the video posted by the 'Yes' campaign, she encouraged the nation to "stand together" and show support to those who need it most.

"To recognise Indigenous peoples in our constitution for the very first time. To give our kids the very best start in life: an equal start in life," she said.

"I'm voting 'yes' and I am asking that all Australians do too. So please stand with me and write 'yes' on October 14."

Ms Freeman's community advocacy has included establishing the Cathy Freeman Foundation in 2007 to support the futures of children and their families in northern Australian communities.

The three-time Olympian, World Champion and Commonwealth Games gold medallist has been honoured for her achievements, including being named 1998 Australian of the Year.

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More recently a grandstand at Sydney's Accor Stadium has been renamed in her honour - the same venue where she lit the flame at the 2000 Olympics opening ceremony and went on to claim gold in the 400m final.

Campaigning on the Voice to Parliament referendum has ramped up in recent weeks as Australians prepare to head to the polls in less than a month.

Other high-profile Australians who have come out in support of the referendum include musicians such as Paul Kelly and John Farnham, who allowed the Yes campaign to use his iconic hit You're The Voice, and sportspeople including tennis champion Evonne Goolagong Cawley, the NRL's Johnathan Thurston and AFL great Eddie Betts.