The New Zealand-born 22-year-old, cousin of former All Black lock Brad Mika, replaces former Australia captain James Horwill for the dead rubber in front of home fans at Sydney Football Stadium.
Highly skilled and a powerful runner, Skelton remains an unfinished product but has excited Sydney crowds in a strong season with Super Rugby’s New South Wales Waratahs.
“During the series we’ve already benefited from giving two other locks, Sam Carter and Luke Jones, their first opportunities for Australia,” coach Ewen McKenzie said in a team statement on Tuesday.
“The experience they gained will prove invaluable in the long-run and now it’s Will’s turn to show us what he has got.
“I’ve been really impressed with his attitude and the contribution he’s made to this team since the beginning of the series.
“He’s obviously got impressive metrics but he also has a big motor and is particularly skillful, so we’re looking forward to seeing how he will impose himself on the game.”
Skelton’s promotion sees Horwill relegated to the bench again, having regained a starting spot in the wake of Carter’s series-ending injury.
Wycliff Palu returns from a minor ankle injury to number eight after missing the second test in Melbourne, replacing Western Force backrower Ben McCalman.
Australia wrapped up the series with a dour 6-0 win at Docklands Stadium on Saturday which triggered a hail of criticism for the stodgy, territorial game the home side executed.
McKenzie has resisted shaking up the backline which failed to score a try in Melbourne, leaving utility back Kurtley Beale on the bench and sticking with the halves combination of Bernard Foley and Nic White.
Though unapologetic about Saturday’s ugly win, McKenzie defended his record.
“You’re always working towards that complete game where you find the balance between your intentions in attack and an impenetrable defence,” he said.
“Our desire is to always play an up-tempo brand of rugby and we’ve now scored 23 tries in the past six games, an average of almost four a game.
“Our defence has also been steadily improving with each match, culminating with a shut-out of the French in our most recent match in Melbourne.
“The challenge and what we are always aiming for is to put both together and that will be our goal when we return to afternoon rugby in Sydney on Saturday.”
Bidding for their seventh successive win, the Wallabies have made two further changes to the bench, with Rob Horne coming in for fellow centre Pat McCabe and prop Scott Sio replacing Pek Cowan.
Team: 15-Israel Folau, 14-Adam Ashley-Cooper, 13-Tevita Kuridrani, 12-Matt Toomua, 11-Nick Cummins, 10-Bernard Foley, 9-Nic White, 8-Wycliff Palu, 7-Michael Hooper (captain), 6-Scott Fardy, 5-Will Skelton, 4-Rob Simmons, 3-Sekope Kepu, 2-Tatafu Polota-Nau, 1-James Slipper
Replacements: 16-Nathan Charles, 17-Scott Sio, 18-Laurie Weeks, 19-James Horwill, 20-Ben McCalman, 21-Nick Phipps, 22-Kurtley Beale, 23-Rob Horne
(Reporting by Ian Ransom in Melbourne; Editing by Greg Stutchbury)