Voulgaris was born in the island of Hydra to George Voulgaris and Archonto Vatsaxi, a relative of Dimitrios Voulgaris, a former Prime Minister. After the death of his father in 1885, his family settled in Athens, with his mother's relatives. After finishing school, he entered the Hellenic Naval Academy, in 1899, and was commissioned as Ensign in 1903. In 1908–1910 he was detached for training abroad, and he briefly served aboard a French Navy vessel in 1912. He took part in the Balkan Wars aboard the destroyer Panthir, seeing action in the Naval Battle of Elli. In 1915–1916 he served as adjutant to the Navy Minister, Admiral Pavlos Kountouriotis. When the Movement of National Defence broke out in Thessalonica in 1916, the pro-Venizelist Voulgaris, like his mentor and fellow Hydriot Kountouriotis, left Athens and joined the revolutionary government. From 1916 to 1919 he commanded the destroyer Velos, participating in the Allied naval operations in the Aegean during World War I, the 1919 Expedition to the Ukraine, and the opening phase of the Asia Minor Expedition. He subsequently served as head of the private office of the Navy Minister Athanasios N. Miaoulis. Following the anti-Venizelist electoral victory in November 1920, he was suspended in March 1921.
Following the collapse of the Asia Minor front and the revolt by the Army, he was recalled to active service, and appointed captain of the destroyer Leon. In 1923 he became commander of the Faliro Naval Aviation Base, and he subsequently was appointed as captain of the Panthir. Following the so-called "Navy Strike" of June 1924, he resigned from the Navy but was recommissioned two months later. He resigned again a year later, following the coup d'état of General Theodoros Pangalos. Following Pangalos' overthrow in August 1926, he re-joined the service, with the rank of Captain and became Superior Commander of the Naval Aviation, a position he held until 1930. WHen the Air Ministry was established in the same year, he became Director of the Air Force. In 1931, he was appointed commander of the Salamis Naval Base, and in 1931–1934 he served as Supreme Commander of the Submarines. In 1934, he was placed as military attaché to Ankara and Belgrade, based in Istanbul. He was there when the failed Venizelist coup attempt of March 1935 occurred. Being a committed Venizelist, he was suspended and then dismissed by the subsequent purges of the Armed Forces. In November 1935 however, with the return of the monarchy and a partial pardon, he was listed as placed in reserve, with the rank of Rear Admiral of the Reserve.
World War II and aftermath
For the next few years, he worked in the private sector, eventually joining the Bodosakis-Athanasiadis group. He moved to Egypt before the German invasion of Greece in April 1941. In May 1943, the Greek government in exile recalled him to service - alongside many other officers who had been expelled in 1935 - and gave him the post of Aviation Minister. When the Navy mutiny broke out in April 1944, Voulgaris replaced Rear Admiral Konstantinos Alexandris as Chief of the Fleet. From this position he supervised the forced capture of the ships by officer detachments. In October 1944, he led the fleet back to Greece, and assumed the duties of Chief of the Navy General Staff.
The political situation in Greece was extremely unstable: December 1944 saw month-long clashes between government and British forces on one hand and the guerrillas of the National Liberation Front on the other. The Treaty of Varkiza resulted in the latter's disarmament, however, the situation remained volatile. The moderate government of Nikolaos Plastiras resigned under British pressure on 8 April 1945 and the Regent, Archbishop Damaskinos, appointed Voulgaris to head an interim government. Voulgaris also held several other ministries during his two cabinets (the second formed on 11 July), including those of Army, Navy and Air Force, and even, briefly, the Foreign Ministry. Unable to break the political deadlock, Voulgaris resigned his naval commission on 8 October 1945 and, nine days later, also the post of Prime Minister.