The first woman elected to the Sacramento City Council and the first woman to be elected to the city council of any major city in the United States. She was elected as part of a slate of Progressive candidates, defeating the railroad-aligned incumbents. Her campaign had the backing of the Woman's Council, an association of women's clubs she helped found. While in office Johnston focused on education, flood control, street lighting, parks, playgrounds, libraries, cultural facilities, utility rates, and advancement of city morals.