Gyllenstierna was born at Krapperup Castle in Höganäs Municipality, Sweden, the son of landowner, Friherre Nils Gyllenstierna and his wife Ellen (née Stiernstedt) [REF].
He became acting extra head of department at the Ministry for Foreign Affairs on 29 October 1918 and first legation secretary in Helsinki on 12 September 1919 [REF].