The local wildcards won a thriller in Friday's final against Kristina Mladenovic and Manuel Guinard, who were bidding to become the first French duo to win the mixed crown at Melbourne Park.
After splitting the first two sets the Australians triumphed in a 10-point tiebreak decider, running out 4-6 6-4 10-8 winners in 93 minutes.
Doubles specialist Peers served for the win, with Guinard, playing in his first major final, finding the net.
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 again lifted the trophy on Rod Laver Arena.
They became the first pairing to defend their title at Melbourne Park since Czech great Jana Novotna and American Jim Pugh in 1988-89.
And they became the first Australian doubles act to successfully defend, following Margaret Court and Ken Fletcher who won three in a row between 1963 and 1965.
Peers, who also won the US Open mixed title in 2022 and Australian Open men's doubles title Finland's Henri Kontinen in 2017, made a series of uncharacteristic errors in the first set.
But the 37-year-old wasn't alone with five breaks of serve in the opening set with the French winning the key points to surge ahead 5-2 before sealing it 6-4.
Momentum then shifted the home team's way with Peers finding his range and delivering some big serves when it counted to level at one set a piece.
With pressure showing on both pairings, the French edged ahead in the tiebreak 7-5.
But hard-hitting Gadecki held her nerve and then Peers fired a winner to set up two championship points, securing the trophy with the second.
"I can't believe we are in this position right now ... Peersy, thank you for wanting to play with me again this year," said 23-year-old Gadecki, who failed to qualify for the women's singles draw this year.
"Thank you for letting me share the court with you and to hold the trophy again this year is incredible.
"I knew we could do it, but I didn't think we could really do it, if you know what I mean."
Jason Kubler and Marc Polmans will look to follow their lead, through to the men's doubles final where the Australians will take on sixth seeds Neal Skupski of Great Britain and American Christian Harrison for the trophy.
23°C