Þórir came up through the junior ranks of KR and played his first senior game, at the age of 16, on 7 December 2014, when he scored 31 points against Haukar-b in the Icelandic Basketball Cup. During the 2015–2016 season he was named the best young player of the first half of the season. He developed into a key player for KR during its 2017 championship run, averaging 10.2 points, 2.6 rebounds and 1.9 assists per game, and was named the Úrvalsdeild Young Player of the Year after the 2016–17 season.
