Jacks has two caps in the longest format, the last coming against Pakistan in Multan in December 2022, although he is a regular pick in England white-ball teams.
The allrounder has leapfrogged Shoaib Bashir as the first spinner picked in this Ashes after the tourists opted for an all-out pace attack in the first Test in Perth.
Jacks replaces Mark Wood in England's starting line-up after the fast bowler was ruled out through injury.
"It's something I'm really looking forward to," Jacks told the ECB's in-house media. "To be on an Ashes tour in the first place is something I wouldn't have been expecting a few months ago.
"But it's been amazing to be here, be around this team… to be in the XI is a dream come true, to play an Ashes series away from home.
"Personally, I'll just be looking to add a little bit to the team in each three facets of the game. I know I can effect the game in a positive way like that, and I'll just be doing my best to support whenever the team needs me.
"Obviously I play a lot of white ball cricket under lights and hopefully that will suit me and the conditions won't feel too foreign to me. Mostly, I'm just looking forward to getting out there and trying to do my best."
England are 1-0 down in the five-match series having lost by eight wickets inside two days in the first Test in Perth.
England XI: Zak Crawley, Ben Duckett, Ollie Pope, Joe Root, Harry Brook, Ben Stokes (captain), 7 Jamie Smith (wk), Will Jacks, Gus Atkinson, Brydon Carse, Jofra Archer
Australia took control of the second Ashes Test after the third day following a lower-order batting fightback and then taking six England wickets before the close of play.
Australia went to stumps on the second day of the pink ball Ashes Test on 378-6, the home side leading England by 44 runs on the first innings with four wickets still remaining.
England captain Ben Stokes has come out and said he will accept criticism for his team's performance in the first Ashes Test but has pushed back at jibes that the tourists are "arrogant".
Joe Root is confident that he is putting in the right preparation ahead of England's pink ball Ashes Test against Australia that starts in Brisbane on Thursday.
