In 1939, Bitsios entered service in the Greek Foreign Ministry. He served as consul in Cairo, Egypt and later in London. In 1961, he became the permanent Ambassador of Greece to the UN. In 1966, he left that post to head the political office of King Constantine II, a position he quit after the coup d'etat of April 21, 1967. Bitsios then re-entered the diplomatic corps which he quit in 1972.
After the restoration of democracy to Greece in 1974, Bitsios was appointed Deputy Foreign Minister of the national unity government of Constantine Karamanlis. After the latter's victory in the elections of November 1974, he served as Foreign Minister until 1977.
He co-authored five books:
- "Η Μεγάλη Ιδέα του Ελληνισμού" (The Great Idea of Hellenism)
- "Αίγυπτος και Εγγύς Ανατολή" (Egypt and the Near East)
- "Κρίσιμες ώρες" (Critical Times)
- "Φύλλα από ένα ημερολόγιο" (Pages from a Diary)
- "Πέρα από τα σύνορα" (Beyond the Border)