After becoming champions last year with a win over compatriots Kimberly Birrell and John-Patrick Smith in the first all-Australian decider in 58 years, Peers and Gadecki have given themselves an opportunity to defend their crown.
In a gripping semi-final on Wednesday, Peers and Gadecki downed American Taylor Townsend and Croatian Nikola Mektic 7-6 (7-2) 2-6 13-11 on Margaret Court Arena.
The wildcard pairing secured the first set in a tiebreak, before their rivals forced the match into a 10-point tiebreak decider.
But Peers and Gadecki, who are separated in age by 14 years, always had the upper hand in the match tiebreak.
They will meet French pair Kristina Mladenovic and Manuel Guinard in the final after they eliminated second seeds Marcelo Arevalo and Luisa Stefani 6-3 3-6 10-7.
If Gadecki and Peers are able to lift the crown again, they will become the first pairing to defend their title at Melbourne Park since Czech great Jana Novotna and American Jim Pugh in 1988-89.
"It's incredible when you start hearing some of those records you pinch yourself," Peers said.
"Hopefully we can bring our best stuff right in the end.
"She's (Gadecki) pretty good, isn't she.
"We just keep hanging out there."
Gadecki, who failed to qualify for the women's singles in Melbourne draw this year, was thrilled by making it back to another decider.
"It's such a pleasure to be court with Peersy," she said.
"He brings out the best in me.
"Peersy told me to keep backing myself and enjoy the moment.
"It would be pretty special to break a couple of records, to get the Gadecki name out there would be pretty cool."
Their triumph last year was the first mixed doubles title by an Australian pair at Melbourne Park in 12 years.
Peers, a doubles specialist, is already a three-time major champion after winning the men's Australian Open in 2017 with Finland's Henri Kontinen.
Jason Kubler and Marc Polmans, who knocked out Nick Kyrgios and Thanasi Kokkinakis in the first round, are through to the semi-finals and will meet Luke Johnson (England) and Poland's Jan Zielinski.