She was born in Kristiania to Niels Anker Stang Schweigaard (1884–1955) and his wife Betty Reimers (1886–1968).

Born as Ragnhild Elisabeth Schweigaard, she married law professor Knut Sejersted Selmer.

[1] During the German occupation of Norway she had been involved in the Norwegian resistance, in illegal radio broadcasting.

On the local political level, Selmer had been a member of Oslo city council during the term 1951–1955.

[1] In 1965, she was appointed Minister of Justice and the Police as a part of the centre-right cabinet of Per Borten, the first woman to hold this position.