He started training with his local club Dalvík, switching to his father's old club Þór Akureyri for two separate spells before joining German side Hannover's youth team along with his twin brother Þorri Mar Þórisson.[1][2]
In 2018 the brothers returned to their first club Dalvík/Reynir and played with them in the Icelandic 4th tier, with Nökkvi scoring 10 goals in 16 appearances.[3][4][5] The next season they joined KA Akureyri in the Icelandic top tier and Nökkvi played with them for four seasons.[6] In his final season with KA he helped them achieve 2nd place, their best result since winning the league for the only time in 1989, by becoming the top scorer of the 2022 Besta deild karla with 17 goals, despite leaving to join Belgian side Beerschot before the end the season.[7][8] By joining Beerschot, he and his twin brother were now playing for separate clubs for the first time.