At the age of 30, Brandes formulated the principles of a new realism and naturalism, condemning hyper-aesthetic writing and fantasy in literature. According to Brandes, literature should be an organ "of the great thoughts of liberty and the progress of humanity." His literary goals were shared by many authors, among them the Norwegian dramatist Henrik Ibsen. Georg Brandes is widely understood to have inspired the intellectual leftist movement of the inter-war period known as Cultural Leftism.

He was born in Copenhagen in a non-orthodox Jewish middle-class family and became a student at the University of Copenhagen in 1859 where he first studied jurisprudence. From this, however, his interests soon turned to philosophy and aesthetics. In 1862 he won the gold medal of the university for an essay on The Idea of Nemesis among the Ancients. Before this, indeed since 1858, he had shown a remarkable gift for verse-writing, the results of which, however, were not abundant enough to justify separate publication. Brandes did not collect his poems until as late as 1898. At the university, which he left in 1864, Brandes was influenced by the writings of Heiberg in criticism and Søren Kierkegaard in philosophy, influences which continued to leave traces on his work.

In 1866 he took part in the controversy raised by the works of Rasmus Nielsen in a treatise on "Dualism in our Recent Philosophy." From 1865 to 1871 he travelled much in Europe, acquainting himself with the condition of literature in the principal centres of learning. His first important contribution to letters was his Aesthetic Studies (1868), where his maturer method is already foreshadowed in several brief monographs on Danish poets. In 1870 he published several important volumes, The French Aesthetics of the Present Day, dealing chiefly with Taine, Criticisms and Portraits, and a translation of The Subjection of Women by John Stuart Mill, whom he had met that year during a visit to England.

Brandes now took his place as the leading northern European critic, applying to local conditions and habits of thought the methods of Taine. He became docent or reader in Belles Lettres at the university of Copenhagen, where his lectures were the sensational for the time. His famous opening lecture November 3rd 1871 is often considered the gateway of modern Danish literature. On the professorship of Aesthetics becoming vacant in 1872, it was taken as a matter of course that Brandes would be appointed. But the young critic had offended many susceptibilities by his ardent advocacy of modern ideas; he was known to be a Jew, his convictions were Radical, he was suspected of being an atheist. The authorities refused to elect him, but his fitness for the post was so obvious that the chair of Aesthetics remained vacant, no one else daring to place himself in comparison with Brandes.

In the midst of these polemics the critic began to issue the most ambitious of his works, Main Currents in the Literature of the Nineteenth Century, of which four volumes appeared between 1872 and 1875 (English translation, 1901-1905). The brilliant novelty of this criticism of the literature of major European countries at the beginning of the 19th century, and his description of the general revolt against the pseudo-classicism of the 18th century, at once attracted attention outside Denmark. The tumult which gathered round the person of the critic increased the success of the work, and the reputation of Brandes grew apace, especially in Germany and Russia. Among his later writings must be mentioned the monographs on Søren Kierkegaard (1877), on Esaias Tegnér (1878), on Benjamin Disraeli (1878), Ferdinand Lassalle (in German, 1877), Ludvig Holberg (1884), on Henrik Ibsen (1899) and on Anatole France (1905). Brandes wrote with great depth on the main contemporary poets and novelists of his own country and of Norway, and he and his disciples were for a long time the arbiters of literary fame in the north.

His Danish Poets (1877), containing studies of Carsten Hauch, Ludvig Bødtcher, Christian Winther, and Paludan-Müller, his Men of the Modern Transition (1883), and his Essays (1889), are volumes essential to the proper study of modern Scandinavian literature. He wrote an excellent book on Poland (1888; English translation, 1903), and was one of the editors of the German version of Ibsen.

In 1877 Brandes left Copenhagen and settled in Berlin, taking a considerable part in the aesthetic life of that city. His political views, however, made Prussia uncomfortable for him, and he returned in 1883 to Copenhagen, where he found a whole new school of writers and thinkers eager to receive him as their leader. The most important of his recent works has been his study of Shakespeare (1897-1898), which was translated into English by William Archer, and was highly acclaimed. It was, perhaps, the most authoritative work on Shakespeare, not principally intended for an English-speaking audience, which had been published in any country.

He was afterwards engaged on a history of modern Scandinavian literature. In his critical work, which extends over a wider field than that of any other living writer, Brandes was aided by a singularly charming style, lucid and reasonable, enthusiastic without extravagance, brilliant and coloured without affectation. His influence on the Scandinavian writers of the 1880s was very great, but a reaction, headed by Holger Drachmann, against his "realistic" doctrines, began in 1885. In 1900 he collected his works for the first time in a complete and popular edition, and began to work on a German edition, completed in 1902.

After 1890 the disappointed Brandes partly turned away from the direct fight, concentrating around "great personalities" who enlightened the life of their mediocre contemporaries. In this period, he "detected" Friedrich Nietzsche whom he introduced to Scandinavian culture. Brandes, in a 1888 letter, wrote to Nietzsche asking him to read the works of Kierkegaard. He described Nietzsche's philosophy as "aristocratic radicalism", a description which delighted Nietzsche, and the idea of "aristocratic radicalism" influenced most of the later works of Brandes and resulted in voluminous biographies Wolfgang Goethe (1914-15), Francois de Voltaire (1916-17), Gaius Julius Cæsar 1918 and Michelangelo (1921). These books must be considered less original or valid though often written with a dazzling stylistic mastery.

The influence of Brandes faded somewhat after 1900 but he was still considered a leading figure of Danish literary life and his international reputation was growing. In many ways he became a modern Scandinavian Voltaire with a great moral authority, condemning the maltreatment of national minorities, the persecution of Dreyfus etc. During World War I he condemned the national aggression and imperialism on both sides and his last years were dedicated to anti-religious polemic. In this late period he made new connections to intellectuals like Henri Barbusse, Romain Rolland and E. D. Morel.

Today Brandes still stands as one of the most influential inspirations of Danish literature, an equal of Holberg and Grundtvig. This has not prevented him from being criticized. The right wing has condemned him as an unnational and subversive blasphemer and fornicator. On the left wing socialists have criticized his elitist attitudes, while the feminist movement has often regarded his positive attitude of sexual equality as being inconsequential. Nonetheless his influence in Danish cultural history is still far-ranging.

His brother Edvard Brandes (1847-1931), also a well-known critic, was the author of a number of plays, and of two psychological novels: A Politician (1889), and Young Blood (1899). He became an outstanding political figure of the Radical party.