Grimm was born at Ratisbon. He studied at the University of Leipzig, where he came under the influence of Gottsched and of JA Ernesti, to whom he was largely indebted for his critical appreciation of classical literature. When nineteen he produced a tragedy, Banise, which met with some success. After two years of study he returned to Ratisbon, where he was attached to the household of Count Schönberg. In 1748 he accompanied August Heinrich, Count Friesen, to Paris as secretary, and he is said by Rousseau to have acted for some time as reader to Frederick, the young hereditary prince of Saxe-Gotha.
His acquaintance with Rousseau, through a mutual sympathy in regard to musical matters, soon ripened into intimate friendship, and led to a close association with the encyclopaedists. He rapidly obtained a thorough knowledge of the French language, and acquired so perfectly the tone and sentiments of the society in which he moved that all marks of his foreign origin and training seemed effaced. A witty pamphlet entitled Le Petit Prophète de Boehmischbroda (1753), written by him in defence of Italian as against French opera, established his literary reputation. It is possible that the origin of the pamphlet is partly to be accounted for by his vehement passion for Mlle Fel, the prima donna of the Italian company.
In 1753 Grimm, following the example of the abbé Raynal, began a literary correspondence with various German sovereigns. Raynal's letters, Nouvelles littéraires, ceased early in 1755. With the aid of friends, especially of Diderot and Mme d'Epinay, during his temporary absences from France, Grimm himself carried on the correspondence, which consisted of two letters a month, until 1773, and eventually counted among his subscribers Catherine II of Russia, Stanislas Poniatowski, king of Poland, and many princes of the smaller German States.
It was probably in 1754 that Grimm was introduced by Rousseau to Madame d'Epinay, with whom he soon formed a liaison which led to an irreconcilable rupture between him and Rousseau. Rousseau was induced by his resentment to give in his Confessions a wholly mendacious portrait of Grimm's character. In 1755, after the death of Count Friesen, who was a nephew of Marshal Saxe and an officer in the French army, Grimm became secretaire des commandements to the duke of Orleans, and in this capacity he accompanied Marshal d'Estrées on the campaign of Westphalia in 1756–57. He was named envoy of the town of Frankfort at the court of France in 1759, but was deprived of his office for criticizing the comte de Broglie in a dispatch intercepted by Louis XV. He was made a baron of the Holy Roman Empire in 1775.
His introduction to Catherine II of Russia took place at St Petersburg in 1773, when he was in the suite of Wilhelmine of Hesse-Darmstadt on the occasion of her marriage to the czarevitch Paul. He became minister of Saxe-Gotha at the court of France in 1776, but in 1777 he again left Paris on a visit to St Petersburg, where he remained for nearly a year in daily intercourse with Catherine. He acted as Paris agent for the empress in the purchase of works of art, and executed many confidential commissions for her. In 1783 and the following years he lost his two most intimate friends, Mme d'Epinay and Diderot.
In 1792 he emigrated, and in the next year settled in Gotha, where his poverty was relieved by Catherine, who in 1796 appointed him minister of Russia at Hamburg. On the death of the empress Catherine he took refuge with Mme d'Epinay's granddaughter, Emilie de Belsunce, comtesse de Bueil. Grimm had always interested himself in her, and had procured her dowry from the empress Catherine. She now received him with the utmost kindness. He died at Gotha on December 19, 1807.
The correspondence of Grimm was strictly confidential, and was not divulged during his lifetime. It embraces nearly the whole period from 1750 to 1790, but the later volumes, 1773 to 1790, were chiefly the work of his secretary, Jakob Heinrich Meister. At first he contented himself with enumerating the chief current views in literature and art and indicating very slightly the contents of the principal new books, but gradually his criticisms became more extended and trenchant, and he touched on nearly every subject--political, literary, artistic, social and religious--which interested the Parisian society of the time. His notices of contemporaries are somewhat severe, and he exhibits the foibles and selfishness of the society in which he moved; but he was unbiassed in his literary judgments, and time has only served to confirm his criticisms. In style and manner of expression he is thoroughly French. He is generally somewhat cold in his appreciation, but his literary taste is delicate and subtle; and it was the opinion of Sainte-Beuve that the quality of his thought in his best moments will compare not unfavourably even with that of Voltaire. His religious and philosophical opinions were entirely negative.
Grimm's Correspondance littéraire, philosophique et critique ..., depuis 1753 jusqu'en 1769, was edited, with many excisions, by Jean-Baptiste-Antoine Suard and published at Paris in 1812, in 6 vols. 8vo; deuxième partie, de 1771 a 1782, in 1812 in 5 vols. 8vo; and troisième partie, pendant une partie des années 1775 et 1776, et pendant les années 1782 a 1790 inclusivement, in 1813 in 5 vols. 8vo. A supplementary volume appeared in 1814; the whole correspondence was collected and published by Jules Taschereau, with the assistance of A. Chaudé, in a Nouvelle Édition, revue et mise dans un meilleur ordre, avec des notes et des éclaircissements, et oil se trouvent rétablies pour la première fois les phrases supprimées par la censure impériale (Paris, 1829, 15 vols. 8vo); and the Correspondance inédite, et recueil de lettres, poésies, morceaux, et fragments retranchés par la censure impériale en 1812 et 1813 was published in 1829. The standard edition is that of Jean Maurice Tourneux (16 vols., 1877–1882).
Grimm's Mémoire Historique sur l'origine et les suites de mon attachement pour l'impératrice Catherine II jusqu'au décès de sa majesté impériale, and Catherine's correspondence with Grimm (1774–1796) were published by J. Grot in 1880, in the Collection of the Russian Imperial Historical Society. She treats him very familiarly, and calls him Heraclite, Georges Dandin, etc. At the time of the Revolution she begged him to destroy her letters, but he refused, and after his death they were returned to St Petersburg. Grimm's side of the correspondence, however, is only partially preserved. He signs himself "Pleureur." Some of Grimm's letters, besides the official correspondence, are included in the edition of Tourneux; others are contained in the Erinnerungen einer Urgrossmutter of K. von Bechtolsheim, edited (Berlin, 1902) by Count C. Oberndorff.