He was born at Kleinbottwar in Württemberg, and educated at the University of Tübingen and under the influence of Georg Wilhelm Friedrich Hegel. In 1840 he was Privatdozent of theology at Tubingen, in 1847 professor of theology at Berne, in 1849 professor of theology at Marburg, migrating soon afterwards to the faculty of philosophy as the result of disputes with the Clerical party. He became professor of philosophy at the University of Heidelberg in 1862, moved to Berlin in 1872, and retired around 1895. His great work is his Philosophie der Griechen (1844-52). This book he continued to amplify and improve in the light of further research; the last edition appeared in 1902. It was translated into most of the European languages and became the recognized text-book on Greek philosophy.
Zeller also wrote on theology, and published three volumes of philosophical essays. He was also one of the founders of the Theologische Jahrbücher, a periodical which acquired great importance as the exponent of the historical method of David Strauss and Christian Baur. Like most of his contemporaries he began with Hegelianism, but subsequently he developed a system on his own lines. He saw the necessity of going back to Kant in the sense of demanding a critical reconsideration of the epistemological problems which Kant had made but a partially successful attempt to solve.
Nonetheless his merits as an original thinker are far outshone by his splendid services to the history of philosophy. It is true that his view of Greek thought is somewhat warped by Hegelian formalism. He is not alive enough to the very intimate relation which thought holds to national life and to the idiosyncrasy of the thinker. He lays too much stress upon the "concept," and explains too much by the Hegelian antithesis of subjective and objective. Nevertheless his history of Greek philosophy remains a noble monument of solid learning informed with natural sagacity. He received the highest recognition, not only from philosophers and learned societies all over the world, but also from the emperor and the German people. In 1894 the Emperor Wilhelm II made him a "Wirklicher Geheimrat" with the title of "Excellenz," and his bust, with that of Helmholtz, was set up at the Brandenburg Gate near the statues erected to the Emperor and Empress Frederick. He died on the 19th of March 1908.
The Philosophie der Griechen has been translated into English by SF Alleyne (2 vols., 1881) in sections: SF Alleyne, Hist. of Gk. Phil. to the time of Socrates (1881); OJ Reichel, Socrates and the Socratic Schools (1868; 2nd ed. 1877); SF Alleyne and A Goodwin, Plato and the Older Academy (1876); Costelloe and Muirhead, Aristotle and the Earlier Peripatetics (1897); OJ Reichel, Stoics, Epicureans and Sceptics (1870 and 1880); SF Alleyne, Hist. of Eclecticism in Gk. Phil. (1883).
The Philosophie appeared in an abbreviated form as Grundriss der Geschichte der Griechischen Philosophie (1883; 5th ed. 1898); English transl. by Alleyne and Evelyn Abbott (1866), under the title, Outlines of the History of Greek Philosophy. Among his other works are: