Following US President Barack Obama's comments endorsing same-sex marriage, Marie Claire magazine, in conjunction with the Seven Network's Sunrise and Morning Show programs, launched the campaign on Sunday.
"Love is quite commonly referred to as being universal and having no boundaries. With this in mind, I find it quite unbelievable that we can be living in a modern society, in a country like Australia, yet still not have the support from the government to allow all couples the right to be legally bound," Gale says.
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Fellow model Hawkins says everyone should have the right to marry and have a special day.
"Everybody loves the same way, so they should be able to celebrate it in the same way. I have a lot of gay friends, so I want them to be happy," she says.
The July issue of Marie Claire features many well-known faces pledging their support for marriage equality - including TV vet Dr Chris Brown, singer Brian McFadden and Olympic diver Matt Mitcham.
On Thursday the I Do campaigners will hold events in Sydney's Martin Place and Melbourne's Bourke Street Mall, and are inviting the public to sign a petition that will be presented to federal parliament.
"Love is love. If you care about equality for all people - whether you're gay or straight - we need your voice," says Marie Claire publisher/editor Jackie Frank.
Bob Brown, the openly gay former Greens leader, says any couple should be able to make a public commitment of love on an equal basis. "It's a matter of saying that love is equal and it should be promoted and not repressed. People love nothing more than a marriage. The more the merrier."
Mitcham, who is also gay, says: "I wish for every person to have the option to marry if they wish, no matter their sexual orientation. We have emotionally developed as a nation and we are ready for this."
