Miaoulis was born in Negropont. The surname Miaoulis, which was added to his family name of Vokos is said to be derived from the Turkish word miaoul, a felucca. Another possibility is that it came from his customary command to his crewmen to row together ("μία ούλοι!")
He settled in the island of Hydra on the east of the Morea, and when the Greek War of Independence began was known among his fellow townsmen as a trader in corn who had gained wealth, and who made a popular use of his money. He had been a merchant captain, and was chosen to lead the naval forces of the islands when they rose against the government of the Sultan.
The islanders had enjoyed some measure of exemption from the worst excesses of the Turkish officials, but suffered severely from the conscription raised to man the Turkish ships; and though they seemed to be peculiarly open to attack by the Sultan's forces from the sea, they took an early and active part in the rising. As early as 1822 Miaoulis was appointed navarch, or admiral, of the swarm of small vessels which formed the insurgent fleet. He commanded the expedition sent to take revenge for the massacre of Chios in the same year.
He continued to be the naval chief of the Greeks till the former Royal Navy officer Thomas Cochrane entered their service in 1827. Miaoulis then retired in order to leave the English officer free to act as commander. In the interval he had had the general direction of the naval side of the Greek struggle for freedom. He had a share in the successful relief of the first siege of Messolonghi in December 1822 and January 1823.
In 1824, after the destruction of Psara by the Turks, he commanded the Greek forces which prevented the further progress of the Sultan's fleet, though at the cost of the loss of many fire ships and men to themselves. But in the same year he was unable to prevent the Egyptian forces from occupying Navarino, though he harassed them with some success. During 1825 he succeeded in carrying stores and reinforcements into Messolonghi, when it was besieged for the second time, though he could not avert its fall.
His efforts to interrupt the sea communications of the Egyptian forces failed, owing to the enormous disproportion of the two squadrons in the siege and strength of the ships. As the war went on the naval power of the Greeks diminished, partly owing to the penury of their treasury, and partly to the growth of piracy in the general anarchy of the Eastern Mediterranean.
When Miaoulis retired to make room for Cochrane, the conduct of the struggle had really passed into the hands of the Great Powers. When independence had been obtained, Miaoulis in his old age was entangled in the civil conflicts of his country, as an opponent of Κapodistrias and the Russian party. He had to employ his skill in the employment of fireships against them at Poros in 1831. He was one of the deputation sent to invite King Otto to accept the crown of Greece, and was made rear-admiral and then vice-admiral by him. He died on the 24 June 1835 at Athens and was buried in Piraeus in what is now known as "Miaouli Coast".