Petra Gregorine Fernanda Nissen (née Thomesen; 15 August 1862 – 3 April 1920) was a Norwegian journalist, literary critic, theatre critic, politician and feminist pioneer.

[1] She was married to newspaper editor and politician Lars Holst from 1882 to 1895, and to physician Oscar Egede Nissen from 1895 to 1911.

[1] She belonged to a network of female writers and critics, including Nini Roll Anker, Hulda Garborg and Sigrid Undset.

She represented the Labour Party in Kristiania city council from 1910.

[4] As an Oslo politician she chaired the Park committee, and she worked for improving conditions for poor people, especially women and children.