Senior Debut: v Ospreys, October 2011, Thomond Park Stadium
European 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 in the Munster Rugby Academy and was added to the Heineken Cup squad in the 2011/2012 season in his final year.
This was just reward for the impact he had made at British & Irish Cup level and on the number of occasions he featured in RaboDirect PRO12 games.
He moved to a development contract at the start of the 2012/13 season and the Corkman did not have to wait long before making his first Heineken Cup start, excelling in a pool win over Saracens at Thomond Park that December. He then signed a two-year full contract from season 2013/14.
He represented the Ireland U20s in two Junior World Cup campaigns, in Japan in 2009 and in Argentina in 2010, and in June 2013 represented Emerging Ireland in the Tbilisi Cup.
During the 2013/14 he only featured on five occasions due to injury, and had to undergo surgery after injuring the patellar tendon in his right knee against Zebre in February 2014 and closed out his season rehabbing.
Made a return to PRO12 action against Newport Gwent Dragons at Rodney Parade in November '14, and went on to score his first try for Munster against Leinster on St. Stephen's Day in Thomond Park.
Signed a two-year contract extension in December 2015 that sees him remain at the province until at least June 2017.
After hugely impressive performances - 14 in total - a knee injury sustained in April would see him miss the business end of the 2016/17 season.
Returned to full fitness in January 2018, helping Munster A into the quarter-finals of the B&I Cup before making his senior return against Zebre in February. Signed a one-year contract extension in March to keep him at the province until at least June 2019.
Started the opening two PRO14 games of the 2018/19 season but suffered a foot injury playing for Munster A against Leinster A in the Celtic Cup in October.
O'Callaghan departed Munster at the end of the 2018/19 season.