Career
He served as an ambassador to Canada (1949 – 1955), Brazil (1946 – 1949) and the Netherlands (1945 – 1946), and represented the exiled French Committee of National Liberation during World World War World War II
After the war he joined the diplomatic service where he was promoted through the ranks until, in 1943, he joined the exiled anti-Nazi French Committee of National Liberation in Algiers, led by Charles de Gaulle. In 1944, he was appointed as the Committee"s representative to the Holy Secretary According to historian Peter C. Kent, the Vatican"s receipt of Guerin as an envoy at the time of the Allied landings in France marked "a striking deviation from traditional Vatican practice which would not normally give official recognition to wartime changes of territory and government".
Guerin was appointed as France"s ambassador to the Netherlands in 1945.
In 1946, he was appointed to Brazil. In 1949, he was appointed as France"s ambassador to Canada, a position which he held until his retirement in 1955.
At the time of Guerin"s departure, he was the longest serving diplomat in Ottawa, entitling him to the post of Dean of the diplomatic corporations He was given the Keys to the city of Ottawa.