Van Roijen's diplomatic career began in the 1930s when he joined the Dutch Ministry of Foreign Affairs in 1930 and was an attache in Washington for three years.
He also held positions in embassies in Tokyo as well as positions at the Ministry of Foreign Affairs in the Hague.
 In 1939, he was named head of the political division at the ministry.

Following the war, he represented the Netherlands at various conferences linked to the nascent United Nations, including the United Nations Conference on International Organization in San Francisco.

After his brief stint as the Dutch foreign minister, he was the ambassador to Canada (1947–1950), to the United States (1950–1964), and jointly to the United Kingdom and to Iceland (1964–1970).
Van Roijen's diplomatic career began in the 1930s when he joined the Dutch Ministry of Foreign Affairs in 1930 and was an attache in Washington for three years. He also held positions in embassies in Tokyo as well as positions at the Ministry of Foreign Affairs in the Hague.  In 1939, he was named head of the political division at the ministry.
Following the war, he represented the Netherlands at various conferences linked to the nascent United Nations, including the United Nations Conference on International Organization in San Francisco.
After his brief stint as the Dutch foreign minister, he was the ambassador to Canada (1947–1950), to the United States (1950–1964), and jointly to the United Kingdom and to Iceland (1964–1970).
Herman van Roijen