The restoration of Russian and Turkish authority shortly afterwards drove him into exile. He took refuge in Paris, and endeavoured to influence French opinion in favour of the proposed union and autonomy of the Danubian principalities. In 1854, however, he was sentenced to a fine of £120 and three months' imprisonment for sedition, and later confined in a lunatic asylum; but in 1856 he returned home with his brother, Dimitrie Brătianu, afterwards one of his foremost political opponents. During the reign of Alexandru Ioan Cuza (1859-1866), Brătianu figured prominently as one of the Liberal leaders. He assisted in 1866 in the deposition of Cuza and the election of Prince Charles of Hohenzollern, under whom he held several ministerial appointments during the next four years. He was arrested for complicity in the revolution of 1870, but soon released.
In 1876, aided by C. A. Rosetti, be formed a Liberal cabinet, which remained in power until 1888. For an account of his work in connexion with the Russo-Turkish War of 1877, the Berlin congress, the establishment of the Romanian kingdom, the revision of the constitution, and other reforms. After 1883 Brătianu acted as sole leader of the Liberals, owing to a quarrel with C. A. Rosetti, his friend and political ally for nearly forty years. His long tenure of office, without parallel in Romanian history, rendered Brătianu extremely unpopular, and at its close his impeachment appeared inevitable. But any proceedings taken against the minister would have involved charges against the king, who was largely responsible for his policy; and the impeachment was averted by a vote of parliament in February 1890.
Besides being the leading statesman of Romania during the critical years 1876-1888, he attained some eminence as a writer. His French political pamphlets, Mémoire sur l'empire d'Autriche dans la question d'Orient (1855), Réflexions sur la situation (1856), Mémoire sur la situation de la Moldavie depuis le traité de Paris (1857), and La Question religieuse en Roumanie (1866), were all published in Paris.