Senior Debut: v Ospreys, October 2011, Thomond Park Stadium
Heineken Cup Debut: v Northampton Saints, January 2012, Milton Keynes
Previous Club: UCC
School: Midleton College
International Honours: Ireland U18/U20, Emerging Ireland
O'Callaghan spent three years at the Munster Rugby Academy and was added to the Heineken Cup squad in the 2011/2012 season.
This was just reward for the impact he'd made at British & Irish Cup level and on the number of occasions he featured in RaboDirect PRO12 games.
The Corkman had to wait until the end of 2012 for his first Heineken Cup start, excelling in a pool win over Saracens at Thomond Park.
He represented the Ireland U20s in two Junior World Cup campaigns, in Japan in 2009 and in Argentina in 2010.
O'Callaghan signed a new contract at the beginning of 2013 that will keep him at Munster until at least 2015.
The Cork man had to undergo surgery after injuring the patellar tendon in his right knee against Zebre in February 2014.