Hammarskjöld was born on 22 April 1865 at Väderum farm in Tuna Parish, Vimmerby Municipality, Sweden, the son of lieutenant Knut Hammarskjöld and Wilhelmina Mimmi . Carl Gustaf Hammarskjöld was brother to Hjalmar Hammarskjöld, cousine to Carl Hammarskjöld and Hugo Hammarskjöld, all of which were born in the same room, on the same farm, and became all ministers. Carl Gustaf was uncle to Dag Hammarskjöld.
Career
Hammarskjöld was commissioned as an officer in Värmland Rifle Corps in 1885 with the rank of underlöjtnant. He was promoted to lieutenant in 1891 and served as a staff adjutant and lieutenant in the General Staff in 1895. Hammarskjöld was promoted to captain in the army and in the General Staff in 1899 and he served as a teacher at the Royal Swedish Army Staff College from 1899 to 1903. He then served as captain in Vaxholm Grenadier Regiment in 1903 and as a general staff officer in the staff of the 2nd Army Division from 1903 to 1905. Hammarskjöld served as chief of staff in the 1st Army Division from 1905 to 1906 then he was promoted to major in the General Staff and appointed vice chief of the Military Office of the Ministry of Land Defence. In 1910, Hammarskjöld was promoted to lieutenant colonel in the 1st Life Grenadier Regiment. Hammarskjöld was secretary in several military committees and assisted the General Staff in drafting proposals for a new conscript law in 1911 and experimental mobilization in 1912. He was promoted to colonel in the army in 1913. In the Ministry of Land Defence from 1913 to 1914, he drafted a proposal for a new conscript law and a new army order. He was also an expert in the same ministry regarding commissariat equipment for the Landstorm. He then served as commander of the 1st Life Grenadier Regiment from 1914 and of the 3rd Infantry Brigade from 1 January 1917. Hammarskjöld was promoted to major general and appointed commanding officer of the 6th Army Divison in 1919. In 1919, Hammarskjöld became a member of the Committee on Defense Audit. Hammarskjöld served as Minister of Defence and head of the Ministry of Defence from 27 October 1920 to 6 June 1921. He then served eight years, from 1922 to 1930 as Chief of the General Staff. He was promoted to lieutenant general in 1926 and to full general then he retired from the military in 1930. Hammarskjöld transferred to the reserve and remained there until 1937. Hammarskjöld was a member of Andra kammaren 1918 to 1920, and of the Första kammaren from 1924 to 1932, representing Lantmanna- och borgarpartiet.
