Kristinn started his career with local club Fjölnir before signing with Valur at 21 years old. In the 2016 season, he was named Players' Player of the Year in the Icelandic league, Úrvalsdeild.[1]
In 2017, he signed with GIF Sundsvall in the Swedish Allsvenskan.[2][3][4][5] He played 27 league games, scoring once,[6] before leaving by mutual consent at the end of the season.[7]
In the winter of 2022 it was announced thak Kristinn would be joining Icelandic giants Valur for the third time in his career.[8]