From 1919 he represented the
National Progressive Party. Holsti represented Finland in the
League of Nations. He was also a republican (opposing the then ongoing movement for monarchy in Finland). A firm supporter of democracy, he openly criticized
Adolf Hitler at the outbreak of war. He held a pro-British political stance. Holsti worked for newspapers in
Hämeenlinna,
Lahti and Helsinki together with his friend and school companion
Joel Lehtonen. The friendship ended abruptly when Holsti recognized himself as the satirically portrayed and fictive politician Rolf Idell in Lehtonen's book
Sorron lapset (1924). Holsti was also Envoy to
Estonia from 1923 to 1927.{{cite web|url=http://www.finland.ee/public/default.aspx?nodeid=40606&contentlan=13&culture=et-EE|title=Ajalugu|publisher=Embassy of Finland, Tallinn Later in life, Holsti taught at
Stanford University, after he moved to
United States with his two sons:
Kalevi and
Olavi Holsti (both respected political scientists in their own right). He maintained a healthy correspondence with president
Herbert Hoover, and the prime minister and president of Finland. He died on 3 August 1945 at Palo Alto Hospital while undergoing surgery to repair a hernia. His wife Liisa died of tuberculosis on 22 July 1951. ==Honorary degrees==