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
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.
Stand-in captain Steve Smith struggled to contain his admiration after Travis Head's blistering 123 off 83 balls sealed Australia's two-day victory in the first Ashes Test in Perth.
England captain Ben Stokes admitted his side were left "shellshocked" after Travis Head's blistering century powered Australia to an eight-wicket victory inside two days in the opening Ashes Test in Perth.
