Having graduated from secondary school in Gothenburg, she studied in Falun, and worked as a teacher, first in Värmland and later in Täby, north of Stockholm, where she was a member of the local council from 1963 to 1971.

Söder's party left the government in 1978 over a conflict on nuclear power, and she was succeeded by liberal Hans Blix.

In 1979 the Centre Party rejoined the coalition, and Söder returned to the Cabinet as Minister of Health and Social Affairs in 1979.

During her years in politics, she also held posts as chairperson of Save the Children Sweden 1983–1995 and as President of the Nordic Council 1984–1985 and 1989–1990.

Despite her varied accomplishments, the political legacy Söder is most known for among Swedes may be the 1980 reform that shut the stores of Systembolaget, the national alcoholic beverage retailing monopoly, on Saturdays.