He started his manager career with Grótta in the third tier of Icelandic football in 2018, placing second and getting promoted. In the 2019 second tier season he guided Grótta to first place in the league and promotion to the top tier. After the season he was hired by Breiðablik, with Grótta hiring Ágúst Gylfason who had just vacated the manager role at Breiðablik.[4] In 2019 Óskar Hrafn was voted the coach of the year in Icelandic sports as the Icelandic Sportsperson of the Year was announced.[5]
In October 2023, Norwegian Eliteserien club Haugesund announced that Óskar would become head coach starting from the 2024 season.[6] In May 2024, he resigned after only seven matches in charge of the club.[7]