His father, Garðar Gíslason, is a teacher; his mother, Kolbrún Högnadóttir, worked for the publisher Fróði.

[2][3] For many years he was a gymnast, competing for the Icelandic, Norwegian, and Danish national teams and belonging to the elite Ármann club together with Guðjón Guðmundsson, who was national champion in his age group for several years;[4] he considered becoming a gymnastics coach but found it unappealing.

The production's success led to an invitation to transfer it to the Young Vic in London, from where it moved in 2004 to the Playhouse Theatre.

[5] He has since directed further stage productions, including an adaptation of Kafka's The Metamorphosis in association with David Farr and the Lyric Theatre, Hammersmith, which toured in many European countries and the US in addition to the UK and Iceland.

[2] In 2023, a non-replica version of the musical "Frozen" based on the Disney Film of the same name directed by Gísli Örn opened at Det Norske Teatret starting a tour in all Scandinavia, this new version had a nordic vision changing sets and orchestrations to match the culture better.