She spent the 2017–2018 season with Olympique de Marseille in the French Division 1 Féminine and has previously played in the Úrvalsdeild kvenna for Breiðablik and the Norwegian Toppserien for Kolbotn and Arna-Bjørnar.

[2][3][4] After eight seasons at the Icelandic Úrvalsdeild kvenna with Breiðablik, where she scored 50 goals in 107 league matches, Fanndís decided to join Norwegian Toppserien club Kolbotn, signing a year contract on 6 December 2012.

[10] In August 2017, she became the first Icelandic female player to join a French Division 1 Féminine club[11] by signing a year contract to play for Olympique de Marseille.

[19] After playing the 2013 Algarve Cup and friendly matches, national team coach Siggi Eyjólfsson selected Fanndís in the Iceland squad for the UEFA Women's Euro 2013.

[19] Fanndís scored her second brace for the national team during Iceland opening match of the 2019 FIFA Women's World Cup qualification on 18 September 2017 in an 8–0 win over Faroe Islands, it took her tally to 13 goals.