Two months later, when all Italy and half the rest of Europe were in the throes of revolution, the people forced Count Pallfy (Erdődy Pállfy Alajos gróf), the Austrian governor, to release him (17 March). The Austrians soon lost all control of the city: the arsenal was seized by the revolutionaries and, under the direction of Manin, a civic guard and a provisional government were instituted. The Austrians evacuated Venice on 26 March and Manin became president of the re-created Republic of San Marco. He was already in favor of Italian unity, and though not anxious for annexation to Piedmont (he would have preferred to invoke French aid), he gave way to the will of the majority, and resigned his powers to the Piedmontese commissioners on 7 August. But after the Piedmontese defeat at Custoza, and the armistice by which King Charles Albert abandoned Lombardy and Venetia to Austria, the Venetians attempted to lynch the royal commissioners, whose lives Manin saved with difficulty; an assembly was summoned, and a triumvirate formed with Manin at its head.

Towards the end of 1848 the Austrians, having been heavily reinforced, reoccupied all the Venetian mainland. The citizens, however, hard - pressed and threatened with a siege, showed the greatest devotion to the cause of freedom, all sharing in the dangers and hardships and giving what they could afford to the state treasury. Early in 1849 Manin was again chosen president of the Republic, and conducted the defense of the city with great ability.

After the defeat of Charles Albert's troops at Novara in March, the Venetian assembly voted "Resistance at all costs!" and granted Manin unlimited powers.

Meanwhile the Austrian forces closed round the city. Manin showed a good capability of organization, in which he was ably seconded by the Neapolitan general, Guglielmo Pepe, who led the Neapolitan army to defend Venice against his king's order. But on 26 May the Venetians were forced to abandon Fort Marghera, half - way between the city and the mainland; food was becoming scarce, on 19 June the powder magazine blew up, and in July cholera broke out. The Austrian batteries, subsequently, began to bombard Venice itself, and when the Sardinian fleet withdrew from the Adriatic the city was also attacked by sea, while demagogues caused internal trouble.

At last, on 24 August 1849, when all provisions and ammunition were exhausted, Manin, who had courted death in vain, succeeded in negotiating an honorable capitulation, on terms of amnesty to all save Manin himself, Pepe and some others, who were to go into exile. On 27 August Manin left Venice forever on board a French ship.

His wife died at Marseille, and he himself reached Paris broken in health and almost destitute, having spent all his fortune for Venice.

In Paris he maintained himself by teaching and became a leader among the Italian exiles. There he became a convert from republicanism to monarchism, being convinced that only under the auspices of King Victor Emmanuel could Italy be freed, and together with Giorgio Pallavicini and Giuseppe La Farina he founded the Società Nazionale Italiana with the object of propagating the idea of unity under the Piedmontese monarchy.

His last years were embittered by the terrible sufferings of his daughter, who died in 1854. He died on 22 September 1857, and was buried in Ary Scheffer's family tomb.

In 1868, two years after the Austrians finally departed from Venice, his remains were brought to his native city and honored with a public funeral.
Manin was a man of the greatest honesty, and possessed genuinely statesmanlike qualities. He believed in Italian unity when most men, even Cavour, regarded it as a vain thing. For example, during the 1856 Congress of Paris, Manin met with Cavour to discuss the unification of Italy. After the meeting, Cavour wrote that Manin had talked about "l'unità d'Italia ed altre corbellerie" ("the unity of Italy and other nonsense"). Manin's work of propaganda by means of the Italian National Society greatly contributed to the success of the cause.