The international trio will bring 302 caps' worth of provincial experience to the Leinster team, who face the Lions at Ellis Park on Saturday (kick-off 1.30pm local time/12.30pm Irish time).
Ryan Baird will make his first competitive appearance since last April's Investec Champions Cup quarter-final win over Sale Sharks. He joins forces with Conor O'Tighearnaigh at lock.
Following his return to full training, Andrew Porter will pack down at tighthead, alongside Gus McCarthy and Alex Usanov. A calf injury kept Porter out of Ireland's Nations Championship Southern Hemisphere Series.
Max Deegan will captain the province from blindside flanker, as he did for their recent 56-12 pre-season win over Zebre Parma which christened the newly-named and redeveloped Laya Arena.
Alongside Deegan in the back row will be Scott Penny and Old Belvedere clubman Josh Ericson, who is rewarded with his first start at number 8 - and his fourth appearance at this level.
Out of action since June due to a groin injury, Tommy O'Brien slots back in on the right wing, Andrew Osborne is on the left, and Academy full-back Todd Lawlor makes his debut as a starter.
Another talented 20-year-old, Academy out-half Caspar Gabriel, is handed his first senior start at half-back, pairing up with the 33-times capped Fintan Gunne.
Head coach Leo Cullen has opted for Hugh Cooney and Charlie Tector as the starting centres, as Leinster face the Lions for the first time since last May's 59-10 victory at the URC's quarter-final stage.
Centurion prop Peter Dooley is set for his first Leinster appearance since rejoining the province from Connacht. Also on the bench is first-year Academy lock Dylan McNeice, who is the second new cap involved.
Stephen Smyth, Niall Smyth, and Brian Deeny are the other forward reinforcements, while the back-line options are Oliver Coffey, Harry Byrne, and Academy youngster Ciarán Mangan (21).
Ahead of the Johannesburg clash, which will be broadcast live on TG4 and Premier Sports 1, Cullen said: "There's a couple of guys who will be making their debuts for Leinster this weekend which is hugely exciting.
"We have three Academy players in the starting XV, another three Academy players on the bench this week, and we've three other Academy players in the wider squad.
"It is only positive for the future of the club. What better place to test yourself than away here in South Africa. The home of the World champions.
"Anyone who would watch the Lions - especially when they play here at Ellis Park - all across the course of last season and how dangerous they are and how they play the game.
"It's a serious challenge for our guys and they've been made well aware of it over the course of pre-season. We're all curious to see how they get on now."
Meanwhile, new signing Joey Carbery, who returned to the province over the summer, has stepped up his training involvement this week as part of his return from an ACL injury.
Jamison Gibson-Park (minor groin injury), Cormac Foley (calf), Jordan Larmour (calf), Diarmuid Mangan (foot), and James Culhane (hamstring) are all unavailable for selection.
LEINSTER (v 10bet Lions): Todd Lawlor; Tommy O'Brien, Hugh Cooney, Charlie Tector, Andrew Osborne; Caspar Gabriel, Fintan Gunne; Alex Usanov, Gus McCarthy, Andrew Porter, Ryan Baird, Conor O'Tighearnaigh, Max Deegan (capt), Scott Penny, Josh Ericson.
Replacements: Stephen Smyth, Peter Dooley, Niall Smyth, Brian Deeney, Dylan McNeice, Oliver Coffey, Harry Byrne, Ciarán Mangan.
