The inclusion of the former Melbourne Storm premiership winger is among a swag of changes to the Australian line-up for the sold-out SCG clash, with Reds backrower Harry Wilson and Melbourne fullback Reece Hodge named in the starting side.
Coach Dave Rennie has made four changes to the starting XV with lock Nick Frost earning his first Test start and James Slipper returning to the familiar loosehead prop role in place of Angus Bell.
Returning to the SCG to play a Test for the first time since 1986, the Wallabies are looking to hoist aloft the newly minted Ella-Mobbs trophy, with the series locked at one win apiece.
Vunivalu switched codes ahead of the 2021 Super Rugby season but the Reds flyer battled ongoing hamstring trouble which limited his chances to push for Test selection.
Hodge is the Wallabies' third starting fullback in as many games - Tom Banks and Jordan Petaia have been sidelined with injury - and will be joined in the back three by wingers Tom Wright and Marika Koroibete.
Wilson will start at blindside flanker with skipper Michael Hooper and No.8 Rob Valetini rounding out the backrow. Rob Leota is now among the reserves.
Frost will combine with Rebels stalwart Matt Philip in the second row.
Brumbies duo Nic White and Noah Lolesio will partner in the halves for the third consecutive match, with the former set to bring up his 50th appearance in the gold jersey.
Reds skipper Tate McDermott has also earned his first call-up of the series, named on the bench while centre Len Ikitau will make his return from calf soreness via the reserves.
"Harry and Reece are both super excited to wear the Wallaby gold for the first time this year and have trained extremely well," Rennie said on Thursday.
"We know we're a much better team than how we played in Brisbane and we've had a good week of preparation.
"As a squad we have an opportunity to go to Sydney and lift some silverware in a series decider and that's something that highly motivates us."
Wallabies: Reece Hodge, Tom Wright, Hunter Paisami, Samu Kerevi, Marika Koroibete, Noah Lolesio, Nic White, Rob Valetini, Michael Hooper, Harry Wilson, Nick Frost, Matt Philip, Taniela Tupou, David Porecki, James Slipper. Reserves: Folau Fainga'a, Angus Bell, Allan Alaalatoa, Rob Leota, Pete Samu, Tate McDermott, Len Ikitau, Suliasi Vunivalu.
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