Marshall and Jackson will form an Ulster 10-12-13 combination with the three-times capped Darren Cave, while Munster prop Kilcoyne will be on familiar territory at Thomond Park.
The 20-year-old Iain Henderson, fresh from his first cap against South Africa, joins continuing captain Jamie Heaslip in the back row, while flying 21-year-old winger Craig Gilroy's last outing in green saw him score two tries and set up another against the Barbarians last May.
Kilcoyne's provincial colleague Denis Hurley, stationed at full-back, is the elder statesman of this bubbly back-line at 28, with forwards Mike Ross (32) and Donncha O'Callaghan (33) the only players in the side past the 30 mark.
Alluding to the high spirits in camp and an infectious enthusiasm that has prevailed all week, head coach Declan Kidney is confident that this matchday 23 can post the first home win of the GUINNESS Series.
"Nobody likes losing a match but the spirit is actually really good. The lads will have a better answer to that than myself but I couldn't be asking any more of them," he said at the team announcement press conference on Thursday.
"There hasn't been a second in training where they've slackened off in terms of work-rate. Their enthusiasm is actually quite infectious.
"Training has been brilliant and the craic around the camp is the same as it always is. There are too many pros there who don't want to be just playing matches and getting losses."
On selection matters, the Corkman said he knew within the first minutes of Monday's training session at Carton House that these young guns deserved a shot at the touring Fijians.
"We know that it will be a full test for us and it's a vote of confidence in the fellas that we've picked.
"These lads who are playing have been training really well over the course of the last two-and-a-half weeks and we feel they deserve their go.
"You have this feeling in the lead-up to matches and fellas would feel good about it but when you get to five minutes before kick-off and the referee's calling you and you go into that 'oh crap' moment and they have to take a deep breath and go for it, that's what I'm really looking forward to seeing.
"And if these lads do what they've been doing week in, week out in a green jersey, then brilliant for us."
Number 8 Heaslip is pleased with how this inexperienced bunch has quickly gelled together as they bid to give Ireland a winning lead-in to the Series finale against Argentina.
"We've looked at what we did right and what we did wrong against South Africa and then started focusing on Fiji," he explained.
"With their Sevens pedigree, we know they like an expansive game. At times the game can get a little bit fractured which they thrive on.
"But we have to focus on ourselves, our structures and patterns. We've to concentrate on the basics because of the new faces and that's what we've been doing this week.
"We hit the ground running on Monday and everyone's been really focused. I can't wait to get out there."
Ireland's most recent encounter with Fiji was a full Test at the RDS three years ago. Kidney's men ran in five tries through Keith Earls (2), Brian O'Driscoll, Rob Kearney and Shane Horgan in a 41-6 success.