O'Callaghan made 8 starts last season in the RaboDirect PRO12 and was added to Munster's Heineken Cup squad to make his Euro debut as a replacement in the win over Nortampton Saints. This term he's been the starting 6 against Treviso and Ulster delivering performances that have put him firmly in Kidney's sightline. 

Ireland squad (33): Rory Best (Banbridge – Ulster), Tommy Bowe (Belfast Harlequins – Ulster), Darren Cave (Belfast Harlequins – Ulster), Tom Court (Malone – Ulster), Sean Cronin (Lansdowne – Leinster), Gordon D'Arcy (Lansdowne – Leinster), Keith Earls (Young Munster – Munster), Stephen Ferris (Dungannon – Ulster), Declan Fitzpatrick (Dungannon – Ulster), Cian Healy (Clontarf – Leinster), Jamie Heaslip (Naas – Leinster), Iain Henderson (Queens University – Ulster), Chris Henry (Ballymena – Ulster), Denis Hurley (Dolphin– Munster), Luke Marshall (Ballymena – Ulster), Conor Murray (Garryowen – Munster), Mike McCarthy (Buccaneers – Connacht), Fergus McFadden (Old Belvedere – Leinster), Kevin McLaughlin (St. Mary’s College – Leinster), David O’Callaghan (Dolphin – Munster), Donncha O'Callaghan (Cork Constitution – Munster), Paul O'Connell (Young Munster – Munster), Brian O'Driscoll (UCD – Leinster), Ronan O'Gara (Cork Constitution – Munster), Peter O'Mahony (Cork Constitution – Munster), Eoin Reddan (Lansdowne – Leinster), Mike Ross (Clontarf – Leinster), Donnacha Ryan (Shannon – Munster), Jonathan Sexton (St.Mary’s College – Leinster), Andrew Trimble (Ballymena – Ulster), Dan Tuohy (Ballymena – Ulster), Damien Varley (Garryowen – Munster), Simon Zebo (Cork Constitution – Munster).