He passed his studentexamen in Djursholm in 1921 and earned a Candidate of Law degree from Stockholm University College in 1927.
[1] Grönwall did his clerkship in Linde Judicial District from 1928 to 1930, before he became an attaché at the Ministry for Foreign Affairs in 1930.
[2] He became chairman of Stockholm University College's legal association in 1927 and was an employee of Swedish Law Journal (Svensk juristtidning) from 1941 to 1947.
Grönwall was member of the Foreign Capital Control Office (Flyktkapitalbyrån) from 1945 to 1947 and was a representative in negotiations on trade policy matters in Stockholm in 1945, Washington, D.C. in 1946, Rome in 1948 and in Annecy in 1949.
[1] He was mediator in the Neutral Nations Supervisory Commission in Korea from 1954 to 1955[2] and head of the Swedish Delegation from 25 September 1969 to 31 March 1970.