She has been a member of the Icelandic parliament, the Alþingi, since 2009. Oddný Harðardóttir represents the Samfylkingin party (the social democratic collective front) . In the Nordic Council, Oddný Harðardóttir represents the Social Democratic Group.
In the Alþingi, Oddný Harðardóttir sits on the economy and trade committee and has been vice chair of the Icelandic delegation to the Nordic Council since 2017.
Oddný Harðardóttir was elected as vice president for 2020 at the Nordic Council Session in Stockholm in October 2019.