In 1913, Parlby helped to found the first women's local of the United Farmers of Alberta.
In 1921, she was elected to the Alberta Legislature for the riding of Lacombe, holding the riding for 14 years.
Appointed as minister without portfolio, she was the first woman Cabinet minister in Alberta.
Parlby was one of the Famous Five or Valiant Five, who by means of a court battle known as the Persons Case established that women were "qualified Persons" in the meaning of the Constitution of Canada and therefore entitled to sit in the Senate of Canada.
Like others of the famous five, however, Parlby was an advocate for the eugenics movement in Alberta including the Sexual Sterilization Act and the sexual sterilization of the mentally infirm.
A lifelong advocate for rural Canadian women and children, Parlby was president of the United Farm Women of Alberta from 1916 to 1919.
On behalf of the UFWA, she pushed to improve public health care services and establish municipal hospitals as well as mobile medical and dental clinics.
In 1921, Parlby was elected to the provincial legislature and made a cabinet minister (the second woman in Canada to hold a provincial cabinet post).
She was once quoted saying: "...and what when we die? Should women go back to the state they once belonged to.
No, they should rather take arms against it, and fight for acknowledgment, not uniformity." Here she fought for acceptance rather than equality to the male gender.
She was the last surviving member of the Famous Five.