The Harlequins lock makes the final appearance of his professional career at Twickenham, in charge of a cosmopolitan side from nine different countries.
He starts alongside his Quins team-mate Joe Marler, who started for England last year when they suffered a record 63-45 defeat against the famous invitation side.
Head Coach Pat Lam’s side also includes World Cup winners in New Zealand’s John Afoa, Colin Slade, Malakai Fekitoa and Liam Messam. Lam has four representatives from his Bristol Bears side in Afoa, Charles Piutau, Steven Luatua and Chris Vui.
“I probably didn’t expect it to happen, I know I’m lucky to be here, but I’ve wanted to play for the Barbarians since I became a professional rugby player and to lead them is very special,” said Horwill.
“We’re a very good team, a group of guys who have come together well in the last few days and we have a lot of exciting players I’m looking forward to playing alongside.
“I’ve enjoyed being with people like Charles Piutau, who I’ve played against in Super Rugby and over here, and then big John Afoa is the elder statement leading the charge. If we can get the ball to Charles and guys like big Taqele Naiyaravoro, we won’t be too bad.”
Horwill is the most experienced international in the side with 62 caps for the Wallabies and the Barbarians have a total of 478 Test appearances between them.
Baa-baas teams always include at least one uncapped player and this year it is Mark Atkinson, who starts in midfield after an outstanding Gallagher Premiership campaign with Gloucester.
15 Charles Piutau (Bristol Bears & New Zealand), 14 Niyi Adeolokun (Connacht & Ireland), 13 Malakai Fekitoa (Toulon & New Zealand), 12 Mark Atkinson (Gloucester), 11 Taqele Naiyaravoro (Northampton Saints & Australia), 10 Colin Slade (Pau & New Zealand), 9 Rhys Webb (Toulon & Wales), 8 Viliame Mata (Edinburgh & Fiji), 7 Francois Louw (Bath & South Africa), 6 Steven Luatua (Bristol Bears & New Zealand), 5 Chris Vui (Bristol Bears & Samoa), 4 James Horwill (Harlequins & Australia, captain), 3 John Afoa (Bristol Bears & New Zealand), 2 Richard Hibbard (Dragons & Wales), 1 Joe Marler (Harlequins & England)
16 David Heffernan (Connacht & Ireland), 17 Pierre Schoeman (Edinburgh), 18 Finlay Bealham (Connacht & Ireland), 19 Facundo Isa (Toulon & Argentina), 20 Liam Messam (Toulon & New Zealand), 21 Rhodri Williams (Dragons & Wales), 22 Brock James (Bordeaux Begles), 23 Filipo Nakosi (Toulon)