England name Lee Dickson at scrumhalf for Wallabies clash
Dickson's explosive start to the season for Northampton has seen him win the race to partner Owen Farrell at half-back in what will be only his 10th Test appearance.
Youngs, who won two caps for the British and Irish Lions against Australia in the summer, would have been the more experienced option but head coach Stuart Lancaster has chosen the player in form.
Injuries to Manu Tuilagi and Brad Barritt mean Joel Tomkins will make his Test debut at outside centre, partnering Billy Twelvetrees in midfield.
"I'm delighted for Joel. He's had a great week's training and is ready for his chance," Lancaster said.
"He has played in many high-profile games in his career so far and has a great temperament for the big occasion."
Wing Marland Yarde will also be making his first appearance at Twickenham after scoring two tries on his debut against the Pumas in June.
"Billy Vunipola and Marland Yarde made a big impression in Argentina and it's going to be a special occasion for them to run out at Twickenham in front of 82,000 passionate supporters for the first time," Lancaster said.
One of the toughest selection calls facing Lancaster was in the second row but when Geoff Parling suffered mild concussion during training on Tuesday afternoon, the decision was simplified.
Mako Vunipola profits from Alex Corbisiero's knee injury to start at loosehead, while hooker Dylan Hartley and prop David Wilson have recovered from respective ankle and calf injuries to take their places on the bench.
Australia triumphed 20-14 at Twickenham last November and Lancaster is looking for a successful start to an autumn series which continues against Argentina and concludes against New Zealand.
"We're looking forward to the challenge of playing Australia - they have made great strides under Ewen McKenzie and their new coaching team and they are formidable opponents," Lancaster said.
"It's eight months since we played at our home and we are looking forward to getting back there in what is a very important series for us two years out from the World Cup."
Lancaster insisted that his preference for Dickson over Youngs was based on form alone.
"Form has always been the over-riding factor for me, but Lee also has a lot of credit in the bank," Lancaster said.
"At the start of the season in a competitive position he's the one who's really shined. It's a competitive position but on form alone he deserves it.
"To be picked for this England team you have to be playing well and that's reflected in the selection."
Lancaster urged Lawes to take the initiative at the line-out after Parling was ruled out of the autumn opener.
"You lose a lot of experience with Geoff and I'm disappointed that he's injured," he said.
"But it's time for Courtney to come in and show his leadership in the line out
"Dave Attwood is match fit and adds ballast and size to our bench."
Tomkins is making his Test debut on Saturday and Lancaster is backing the dual code international to adapt quickly to Test rugby.
"Joel's big-game temperament will shine through on the weekend," he said.