Hardenberg was born at Essenroda near Hanover. After studying at Leipzig and Göttingen he entered the Hanoverian civil service in 1770 as councillor of the board of domains (Kammerrat); but, finding his advancement slow, he set out — on the advice of King George III of the United Kingdom — on a series of travels, spending some time at Wetzlar, Regensburg (where he studied the mechanism of the Imperial government), Vienna and Berlin. He also visited France, the Dutch Republic and Great Britain, where he was received kindly by the King. On his return, he married, at his father's suggestion, the Countess Reventlow.
In 1778, Hardenberg was raised to the rank of privy councillor and created a graf (or count). He went back to England, in the hope of obtaining the post of Hanoverian envoy in London; but his wife began an affair with the Prince of Wales, creating so great a scandal that he was forced to leave the Hanoverian service. In 1782 he entered that of the Duke of Brunswick, and as president of the board of domains displayed a zeal for reform, in the manner approved by the enlightened despots of the century, that rendered him very unpopular with the orthodox clergy and the conservative estates. In Brunswick, too, his position was in the end made untenable by the conduct of his wife, whom he now divorced; he himself, shortly afterwards, marrying a divorced woman.
Fortunately for Hardenberg, this coincided with the lapsing of the principalities of Ansbach and Bayreuth to Prussia, owing to the resignation of the last margrave, Charles Alexander, in 1791. Hardenberg, who happened to be in Berlin at the time, was on the recommendation of Herzberg appointed administrator of the principalities (1792). The position, owing to the singular overlapping of territorial claims in the old Empire, was one of considerable delicacy, and Hardenberg filled it with great skill, doing much to reform traditional anomalies and to develop the country, and at the same time labouring to expand the influence of Prussia in South Germany. After the outbreak of the revolutionary wars his diplomatic ability led to his appointment as Prussian envoy, with a roving commission to visit the Rhenish courts and win them over to Prussia's views; and ultimately, when the necessity for making peace with the French Republic had been recognized, he was appointed to succeed Count Goltz as Prussian plenipotentiary at Basel (February 28, 1795), where he signed the treaty of peace.
In 1797, on the accession of King Frederick William III of Prussia, Hardenberg was summoned to Berlin, where he received an important position in the cabinet and was appointed chief of the departments of Magdeburg and Halberstadt, for Westphalia, and for the principality of Neuchâtel. In 1793 Hardenberg had struck up a friendship with Count Haugwitz, the influential minister for foreign affairs, and when in 1803 the latter went away on leave (August-October) he appointed Hardenberg his locum tenens. It was a critical period. Napoleon had just occupied Hanover, and Haugwitz had urged upon the king the necessity for strong measures and the expediency of a Russian alliance; During his absence, however, the king's irresolution continued; he clung to the policy of neutrality which had so far seemed to have served Prussia so well; and Hardenberg contented himself with adapting himself to the royal will. By the time Haugwitz returned, the unyielding attitude of Napoleon had caused the king to make advances to Russia; but the mutual declarations of the 3rd and 25th of May 1804 only pledged the two powers to take up arms in the event of a French attack upon Prussia or of further aggressions in North Germany. Finally, Haugwitz, unable to persuade the cabinet to a more vigorous policy, resigned, and on April 14 1804 Hardenberg succeeded him as foreign minister.
If there was to be war, Hardenberg would have preferred the French alliance, the price Napoleon demanded for the cession of Hanover to Prussia; the Eastern powers would not freely have conceded so great an augmentation of Prussian power. However, he still hoped to gain the coveted prize by diplomacy, backed by the veiled threat of an armed neutrality. Then came Napoleon's contemptuous violation of Prussian territory by marching three French corps through Ansbach; King Frederick William's pride overcame his weakness, and on November 3 he signed with Tsar Alexander I of Russia the terms of an ultimatum to be laid before the French emperor.
Haugwitz was despatched to Vienna with the document; but before he arrived the Battle of Austerlitz had been fought, and the Prussian plenipotentiary had to make terms with Napoleon. Prussia, by the treaty signed at Schönbrunn on December 15 1805, received Hanover, but in return for all her territories in South Germany. One condition of the arrangement was the retirement of Hardenberg,whom Napoleon disliked. He was again foreign minister for a few months after the crisis of 1806 (April-July 1807); but Napoleon's resentment was implacable, and one of the conditions of the terms granted to Prussia by the Treaty of Tilsit was Hardenberg's dismissal.
After the enforced retirement of Stein in 1810 and the unsatisfactory interlude of the feeble Altenstein ministry, Hardenberg was again summoned to Berlin, this time as chancellor (June 6, 1810). The campaign of Jena and its consequences had had a profound effect upon him; and in his mind the traditions of the old diplomacy had given place to the new sentiment of nationality characteristic of the coming age, which in him found expression in a passionate desire to restore the position of Prussia and crush her oppressors. During his retirement at Riga he had worked out an elaborate plan for reconstructing the monarchy on Liberal lines; and when he came into power, though the circumstances of the time did not admit of his pursuing an independent foreign policy, he steadily prepared for the struggle with France by carrying out Stein's far-reaching schemes of social and political reorganization.
The military system was completely reformed, serfdom was abolished, municipal institutions were fostered, the civil service was thrown open to all classes, and great attention was devoted to the educational needs of every section of the community. When at last the time came to put these reforms to the test, after the Moscow campaign of 1812, it was Hardenberg who, supported by the influence of the noble Queen Louise, determined Frederick William to take advantage of General Yorck's loyal disloyalty and declare against France. He was rightly regarded by German patriots as the statesman who had done most to encourage the spirit of national independence; and immediately after he had signed the first peace of Paris he was raised to the rank of prince (June 3, 1814) in recognition of the part he had played in the War of Liberation.
Hardenberg now had a position in that close corporation of sovereigns and statesmen by whom Europe was governed. He accompanied the allied sovereigns to England, and at the Congress of Vienna (1814-1815) was the chief representative of Prussia. But from this time the zenith of his influence, if not of his fame, was passed. In diplomacy he was no match for Metternich, whose influence soon overshadowed his own in the councils of Europe, of Germany, and ultimately even of Prussia itself. At Vienna, in spite of the powerful backing of Alexander of Russia, he failed to secure the annexation of the whole of Saxony to Prussia; at Paris, after Waterloo, he failed to carry through his views as to the further dismemberment of France; he had weakly allowed Metternich to forestall him in making terms with the states of the Confederation of the Rhine, which secured to Austria the preponderance in the German federal diet; on the eve of the conference of Carlsbad (1819) he signed a convention with Metternich, by which--to quote the historian Treitschke--"like a penitent sinner, without any formal quid pro quo, the monarchy of Frederick the Great yielded to a foreign power a voice in her internal affairs."
At the congresses of Aix-la-Chapelle(Aachen), Troppau, Laibach and Verona the voice of Hardenberg was but an echo of that of Metternich. The cause lay partly in the difficult circumstances of the loosely-knit Prussian monarchy, but partly in Hardenberg's character, which, never well balanced, had deteriorated with age. He continued amiable, charming and enlightened as ever; but the excesses which had been pardonable in a young diplomatist were a scandal in an elderly chancellor, and could not but weaken his influence with so pious a Landesvater as Frederick William III.
To overcome the king's terror of Liberal experiments would have needed all the powers of an adviser at once wise and in character wholly trustworthy. Hardenberg was wise enough; he saw the necessity for constitutional reform; but he clung with almost senile tenacity to the sweets of office, and when the tide turned against Liberalism he allowed himself to drift with it. In the privacy of royal commissions he continued to elaborate schemes for constitutions that never saw the light; but Germany, disillusioned, regarded him as an adherent of Metternich, an accomplice in the policy of the Carlsbad Decrees and the Troppau Protocol. He died at Genoa soon after the closing of the Congress of Verona.