In the summer of 2018 he moved to the German Handball Bundesliga to THW Kiel, where he signed a three-year contract.

At the U-18 European Championship 2016 in Croatia Gísli was the most successful Icelandic shooter with 53 goals.

[5] On 26 October 2017 he made his debut for the Icelandic national team in a 31:29-victory against Sweden in friendly.

In 2014 he was selected for the Iceland squad to compete in the 2014 Summer Youth Olympics.

He played two games in the tournament and won a bronze medal with the Icelandic team.