Fichte was the son of a ribbon weaver. Educated at the Pforta school (1774–80) and at the universities of Jena (1780) and of Leipzig (1781–84), he started work as a tutor. In this capacity he went to Zürich in 1788 and to Warsaw in 1791 but left after two weeks' probation.

The major influence on his thought at this time was that of Immanuel Kant (Kant, Immanuel), whose doctrine of the inherent moral worth of man harmonized with Fichte's character; and he resolved to devote himself to perfecting a true philosophy, the principles of which should be practical maxims. He went from Warsaw to see Kant himself at Königsberg (now Kaliningrad, Russia), but this first interview was disappointing. Later, when Fichte submitted his Versuch einer Kritik aller Offenbarung (“An Attempt at a Critique of All Revelation”) to Kant, the latter was favourably impressed by it and helped find a publisher (1792). Fichte's name and preface were accidentally omitted from the first edition, and the work was ascribed by its earliest readers to Kant himself; when Kant corrected the mistake while commending the essay, Fichte's reputation was made.

In the Versuch, Fichte sought to explain the conditions under which revealed religion (religion, philosophy of) is possible; his exposition turns upon the absolute requirements of the moral law. Religion itself is the belief in this moral law as divine, and such belief is a practical postulate, necessary in order to add force to the law. The revelation of this divine character of morality is possible only to someone in whom the lower impulses have been, or are, successful in overcoming reverence for the law. In such a case it is conceivable that a revelation might be given in order to add strength to the moral law. Religion ultimately then rests upon the practical reason and satisfies the needs of man, insofar as he stands under the moral law. In this conclusion are evident the prominence assigned by Fichte to the practical element and the tendency to make the moral requirements of the ego the ground for all judgment on reality.

In 1793 Fichte married Johanna Maria Rahn, whom he had met during his stay in Zürich. In the same year, he published anonymously two remarkable political works, of which Beitrag zur Berichtigung der Urteile des Publikums über die französische Revolution (“Contribution to the Correction of the Public's Judgments Regarding the French Revolution”) was the more important. It was intended to explain the true nature of the French Revolution, to demonstrate how inextricably the right of liberty is interwoven with the very existence of man as an intelligent agent, and to point out the inherent progressiveness of the state and the consequent necessity of reform or amendment. As in the Versuch, the rational nature of man and the conditions necessary for its realization are made the standard for political philosophy.

The philosophy of Fichte falls chronologically into a period of residence in Jena (1793–98) and a period in Berlin (1799–1806), which are also different in their fundamental philosophic conceptions. The former period is marked by its ethical emphasis, the latter by the emergence of a mystical and theological theory of Being. Fichte was prompted to change his original position because he came to appreciate that religious faith surpasses moral reason. He was also influenced by the general trend that the development of thought took toward Romanticism.

In 1793 there was a vacant chair of philosophy at the University of Jena, and Fichte was called to fill it. To the ensuing period belongs his most important philosophical work. In this period he published, among other works: Einige Vorlesungen über die Bestimmung des Gelehrten (1794; The Vocation of the Scholar), lectures on the importance of the highest intellectual culture and on the duties that it imposed; several works on the science of knowledge (Wissenschaftslehre), which were revised and developed continually throughout his life; the practical Grundlage des Naturrechts nach Prinzipien der Wissenschaftslehre (1796; The Science of Rights); and Das System der Sittenlehre nach den Prinzipien der Wissenschaftslehre (1798; The Science of Ethics as Based on the Science of Knowledge), in which his moral philosophy, grounded in the notion of duty, is most notably expressed.

The system of 1794 was the most original and also the most characteristic work that Fichte produced. It was incited by Kant's critical philosophy and especially by his Kritik der praktischen Vernunft (1788; Critique of Practical Reason . . .). From the outset it was less critical, precisely because it was more systematic, aiming at a self-sufficient doctrine in which the science of knowledge and ethics were intimately united. Fichte's ambition was to demonstrate that practical (moral) reason is really (as Kant had only intimated) the root of reason in its entirety, the absolute ground of all knowledge as well as of humanity altogether. To prove this, he started from a supreme principle, the ego, which was supposed to be independent and sovereign, so that all other knowledge was deduced from it. Fichte did not assert that this supreme principle was self-evident but rather that it had to be postulated by pure thought. He followed, thereby, Kant's doctrine that pure, practical reason postulates the existence of God, but he tried to transform Kant's rational faith into a speculative knowledge on which he based both his theory of science and his ethics.

In 1795 Fichte became one of the editors of the Philosophisches Journal, and in 1798 his friend F.K. Forberg (Forberg, Friedrich Karl), a young, unknown philosopher, sent him an essay on the development of the idea of religion. Before printing this, Fichte, to prevent misunderstanding, composed a short preface, “On the Grounds of Our Belief in a Divine Government of the Universe,” in which God is defined as the moral order of the universe, the eternal law of right that is the foundation of all man's being. The cry of atheism was raised, and the electoral government of Saxony, followed by all of the German states except Prussia, suppressed the Journal and demanded Fichte's expulsion from Jena. After publishing two defenses, Fichte threatened to resign in case of reprimand. Much to his discomfort, his threat was taken as an offer to resign and was duly accepted.

Except for the summer of 1805, Fichte resided in Berlin from 1799 to 1806. Among his friends were the leaders of German Romanticism, A.W. and F. Schlegel and Friedrich Schleiermacher. His works of this period include Die Bestimmung des Menschen (1800; The Vocation of Man), in which he defines God as the infinite moral will of the universe who becomes conscious of himself in individuals; Der geschlossene Handelsstaat (also 1800), an intensely socialistic treatise in favour of tariff protection; two new versions of the Wissenschaftslehre (composed in 1801 and in 1804; published posthumously), marking a great change in the character of the doctrine; Die Grundzüge des gegenwärtigen Zeitalters (1806; lectures delivered 1804–05; The Characteristics of the Present Age), analyzing the Enlightenment and defining its place in the historical evolution of the general human consciousness but also indicating its defects and looking forward to belief in the divine order of the universe as the highest aspect of the life of reason; and Die Anweisung zum seligen Leben, oder auch die Religionslehre (1806; The Way Towards the Blessed Life). In this last-named work the union between the finite self-consciousness and the infinite ego, or God, is handled in a deeply religious fashion reminiscent of the Gospel According to John. The knowledge and love of God is declared to be the end of life. God is the All; the world of independent objects is the result of reflection or self-consciousness, by which the infinite unity is broken up. God is thus over and above the distinction of subject and object; man's knowledge is but a reflex or picture of the infinite essence.

The French victories over the Prussians in 1806 drove Fichte from Berlin to Königsberg (where he lectured for a time), then to Copenhagen. He returned to Berlin in August 1807. From this time his published writings were practical in character; not until after the appearance of the Nachgelassene Werke (“Posthumous Works”) and of the Sämmtliche Werke (“Complete Works”) was the shape of his final speculations known. In 1807 he drew up a plan for the proposed new University of Berlin. In 1807–08 he delivered at Berlin his Reden an die deutsche Nation (Addresses to the German Nation), full of practical views on the only true foundation for national recovery and glory. From 1810 to 1812 he was rector of the new University of Berlin. During the great effort of Germany for national independence in 1813, he lectured “Über den Begriff des wahrhaften Krieges” (“On the Idea of a True War”).

At the beginning of 1814, Fichte caught a virulent hospital fever from his wife, who had volunteered for work as a hospital nurse; he died shortly thereafter.