The 23-year-old Tillous-Borde played in Castres' 18-15 Heineken Cup win over Leinster at in December and featured twice for France during the November international, scoring a try against the Pacific Islanders.
With David Skrela (injured), Frederic Michalak and Francois Trinh-Duc all failing to make France's extended tournament squad, Beauxis gets a chance to impress at number 10.
The Stade Francais clubman, who is also 23, has played most of his club rugby at full-back this season but most of his international experience has come at out-half.
Beauxis' last cap was during the 2007 Rugby World Cup and coach Marc Lievremont has taken something of a gamble by pitting the two youngsters together for the trip to Croke Park.
However, Tillous-Borde and Beauxis know each other's games quite well as they were France's half-backs when they won the IRB Under-21 World Championship on home soil in 2006.
In the back-line for Saturday's game, centre Florian Fritz returns for his first Test since February 2007 and his Toulouse club-mate Clement Poitrenaud has gotten the nod at full-back for the first time since the last World Cup.
Predictably, Toulouse, France's only Heineken Cup quarter-finalists, backbone Lievremont's squad by providing eight players, including in-form winger Maxime Medard.
Biarritz back rower Imanol Harinordoquy, one of the most experienced players in the squad, will start ahead of Louis Picamoles at number 8 and will be flanked by the highly-rated Thierry Dusautoir and Fulgence Ouedraogo.
In all, there is just one change to the starting pack which Lievremont selected for France's last international - their 18-13 defeat at the hands of Australia on November 22.
That one switch sees Toulouse prop Benoit Lecouls being preferred to Nicolas Mas on the tighthead side of the scrum.
The French team will once again be captained by Castres lock Lionel Nallet, who is in his second year as skipper.
"We went for experience and power in the front five with a rather mobile back row," Lievremont said.
"We'll have to counter the strength of the Irish at the set pieces. We know it will be a difficult game because the Irish are banking on continuity in their choice of players and style of play."
There are just five survivors from the side which started last year's Six Nations win over Ireland in Paris - Lionel Faure, Dimitri Szarzewski, Nallet, Dusautoir and Ouedraogo - and Lievremont has plumped for a completely different back-line.
Comparing the 2009 team with the one which started France's one and only previous outing at Croke Park in February 2007, there are again only five survivors - Poitrenaud, Yannick Jauzion, Nallet, Sebastien Chabal and Harinordoquy.
FRANCE TEAM & REPLACEMENTS (v Ireland, 2009 RBS 6 Nations Championship, Croke Park, Saturday, February 7, kick-off 5pm):
15 - Clement Poitrenaud (Toulouse) 32 caps
14 - Julien Malzieu (Clermont Auvergne) 6
13 - Florian Fritz (Toulouse) 13
12 - Yannick Jauzion (Toulouse) 55
10 - Lionel Beauxis (Stade Francais) 12
9 - Sebastien Tillous-Borde (Castres Olympique) 4
1 - Lionel Faure (Sale Sharks) 6
2 - Dimitri Szarzewski (Stade Francais) 30
3 - Benoit Lecouls (Toulouse) 5
4 - Sebastien Chabal (Sale Sharks) 42
5 - Lionel Nallet (Castres Olympique) (capt) 41
6 - Thierry Dusautoir (Toulouse) 17
7 - Fulgence Ouedraogo (Montpellier) 11
8 - Imanol Harinordoquy (Biarritz Olympique) 51
16 - Benjamin Kayser (Leicester Tigers) 5
17 - Nicolas Mas (Perpignan) 22
18 - Romain Millo-Chluski (Toulouse) 3
19 - Louis Picamoles (Montpellier) 8
20 - Morgan Parra (Bourgoin) 3
21 - Benoit Baby (Clermont Auvergne) 6
22 - Cedric Heymans (Toulouse) 43