She moved to Sweden in 1939 with her Swedish husband, was successful in films there, also, and became one of the best known Scandinavian actresses of the time period.

During this time she starred in films such as Her Little Majesty (1939), The Case of Ingegerd Bremssen (1942), Ombyte av tåg (1943), Count Only the Happy Moments (1944) and My People Are Not Yours (1944).

Because of her beauty and acting skills, Wigert was approached about becoming a spy for Sweden with the promise to help her get her father released from Nazi prison.

The information Wigert provided to the Nazis was approved ahead of time by the Swedish military.

In response they started a smear campaign about Wigert by telling the public that she was a Nazi collaborator.

Sonja Wigert was married for the first time in 1939–1941 to the Swedish journalist and film scriptwriter Torsten Flodén and a second time from 1945 to the Danish Air Force captain Niels von Holstein-Rathlou (1910–1949), who died when his Supermarine Spitfire fighter crashed in Øresund in 1949.

Sonja Wigert died at age 66, on 12 April 1980, at her home and is buried in L'Alfàs del Pi, north of Benidorm in Spain.