Born in the village of Mandra near Elefsina on 1 January 1887, Sakellariou entered the Hellenic Naval Academy on 4 November 1902 and graduated on 8 July 1906 as a Line Ensign.

[2] As a staunch royalist, he was dismissed from the Navy on 21 June 1917, following the exile of King Constantine I and the assumption of government in Athens by Eleftherios Venizelos.

[2] On 10 November 1920, following the electoral victory of the anti-Venizelist royalist parties, he was recalled to active service; his dismissal was revoked and his sentence was stricken.

[2] From this post he played a key role in the bloodless coup of Georgios Kondylis on 10 October 1935, which quickly abolished the Second Hellenic Republic and restored the monarchy.

He became Chief of the Navy General Staff in January 1937, serving in the post (with a brief interruption in August–September 1938) until the aftermath of the German invasion of Greece in April 1941.

[2] As an active officer, Sakellariou wrote the Greek Navy's sailing manual in 1915, and a historical study on the use of artillery in the late Byzantine Empire (Ιστορία του Πυροβολικού κατά την Δύσιν της Μεσαιωνικής Ημών Αυτοκρατορίας, 1926).

In 1945 he wrote the study Η Θέσις της Ελλάδος εις τον Δεύτερον Παγκόσμιον Πόλεμον on Greece's role during World War II.