Jack Gleeson was born in Cork and raised in Ranelagh, Dublin.

Gleeson attended Trinity College Dublin where He studied philosophy and theology and was a member of DU Players, where he met his future co-founders of Collapsing Horse Theatre Company. Jack Gleeson began acting at the age of 8, in the Independent Theatre Workshop. His first roles were in films such as Reign of Fire (2002), Batman Begins (2005), Shrooms (2007), and A Shine of Rainbows (2009). In 2010, he appeared in a leading role in All Good Children.

Jack Gleeson starred as Joffrey Baratheon in the HBO series Game of Thrones.

Throughout the 2010s, Gleeson was a company member of the Dublin-based Collapsing Horse Theatre Company, of which he was also a founder and producer. He was part of the original cast in the company’s first theatre production Monster / Clock, a children’s theater show which premiered in Dublin in 2012. He also appeared in the company’s ‘lo-fi comedy’ Bears in Space which premiered in Dublin in July 2014 and took part of the 2014 Edinburgh Festival Fringe. The show was well reviewed and had revival productions in Dublin and London in 2015 and off-Broadway in New York in September 2016 as part of Origin’s 1st Irish theatre festival.

In 2019, Gleeson made two public appearances. In June, he was featured in the musical-comedy program AMUSICAL at the Kilkenny Cat Laughs[18] comedy festival in Kilkenny, Ireland with comedians Eleanor Tiernan and Alison Spittle. In August, he made a surprise appearance at Over the Top Wrestling’s Trinity Brawl 2 event in Dublin where he played the face, aptly called ‘TV’s Jack Gleeson,’ opposite Irish wrestler J Money. In March 2020, it was announced Gleeson would return to television, having been cast in a role in Sara Pascoe’s new series Out Of Her Mind.

In August 2021, Jack Gleeson won critical acclaim for his performance as Constantine in the Druid production of The Seagull which was staged on the open air in Coole Park the former estate of Lady Gregory