Returning to Finland, she worked in adult education and served as the General Secretary of the Finnish Ecumenical Council.

She was the daughter of Supreme Administrative Court of Finland President and one-time interim Prime Minister Urho Castrén.

[1] Castrén earned a master's degree in theology and philosophy and entered the foreign service,[2] in the 1940s,[3] serving as Secretary of Foreign Affairs, overseeing women's work and the Finnish Christian Student Association.

[2] She worked in Geneva between 1958[4] and 1962 as the World Student Christian Federation's Secretary to Africa.

[6] Arriving back in Finland, Castrén supervised adult educational learning activities and from 1974-1984 served as the General Secretary of the Finnish Ecumenical Council (SEN).