In 1778 or 1779 he went to Paris and placed himself under Jean-Frédéric Edelmann, a harpsichord player and friend of Méhul's idol Christoph Willibald von Gluck. Méhul's first published composition was a book of pieces for the harpsichord in 1783. He also arranged airs from popular operas and by the late 1780s he had begun to think about an operatic career for himself. In 1787, a certain writer, Valadier, offered Méhul one of his libretti, Cora, which had been rejected by Gluck in 1785. The opera took four years to reach the stage. In the mean time, Méhul had found an ideal collaborator in the shape of the librettist François-Benoît Hoffman, who provided the words to the first of Méhul's operas to be performed, Euphrosine. Its premiere in 1790 was an immense success and marked the composer out as a new talent to be reckoned with. It was also the start of his long relationship with the Comédie Italienne theatre (soon to be renamed the Opéra-Comique). In spite of the failure of Cora which finally appeared the following year and the banning of Adrien for political reasons the year after that, Méhul consolidated his reputation with works such as Stratonice and Mélidore et Phrosine. During the Revolutionary period in France, Méhul composed many patriotic songs and propaganda pieces, the most famous of which is the Chant du départ. Méhul was rewarded by becoming the first composer named as member of the newly founded Institut de France in 1795. He also held a post as one of the five inspectors of the Conservatoire de Paris. Mehul was on friendly terms with Napoleon and became one of the first Frenchmen to receive the Légion d'honneur. Méhul's operatic success was not as great in the first decade of the nineteenth century as it had been in the 1790s, although works such as Joseph (1807) became famous abroad, particularly in Germany. The failure of his opera Les Amazones in 1811 was a severe blow and virtually ended his career as a composer for the theatre. In spite of his friendship with Napoleon, Méhul's public standing survived the transition to the Bourbon Restoration intact. However, the composer was now seriously ill with tuberculosis and he died on October 18 1817.His grave is at the cemetery of Père Lachaise, near the grave of another French composer, his contemporary François-Joseph Gossec.
Méhul's most important contribution to music was his operas. He led the generation of composers who emerged in France in the 1790s, which included his friend and rival Luigi Cherubini and his outright enemy Jean-François Lesueur. Méhul followed the example of the operas which Gluck had written for Paris in the 1770s and applied Gluck's "reforms" to opéra comique (a genre which mixed music with spoken dialogue and was not necessarily at all "comic" in mood). But he pushed music in a more Romantic direction, showing an increased use of dissonance and an interest in psychological extremes such as anger and jealousy, thus foreshadowing later Romantic composers such as Weber and Berlioz. Indeed, Méhul was the very first composer to be styled a Romantic; the Marquis de Condorcet used the term when reviewing Méhul's Le jeune sage et le vieux fou in La chronique de Paris on April 1 1793. His main musical concern was that everything should serve to increase the dramatic impact. As his admirer Berlioz wrote:
[Méhul] was fully convinced that in truly dramatic music, when the importance of the situation deserves the sacrifice, the composer should not hesitate as between a pretty musical effect that is foreign to the scenic or dramatic character, and a series of accents that are true but do not yield any surface pleasure. He was convinced that musical expressiveness is a lovely flower, delicate and rare, of exquisite fragrance, which does not bloom without culture, and which a breath can wither; that it does not dwell in melody alone, but that everything concurs either to create or destroy it - melody, harmony, modulation, rhythm, instrumentation, the choice of deep or high registers for the voices or instruments, a quick or slow tempo, and the several degrees of volume in the sound emitted.One way in which Méhul increased dramatic expressivity was to experiment with orchestration. For example, in Uthal, an opera set in the Highlands of Scotland, he eliminated violins from the orchestra, replacing them with the darker sounds of violas in order to add local colour. Méhul's La chasse du jeune Henri provides a more humorous example, with its expanded horn section portraying yelping hounds as well as giving out the hunting calls. Sir Thomas Beecham frequently programmed this piece to showcase the Philharmonia horn section, led by Dennis Brain. The contemporary listener is still impressed by the pictorial and dramatic effects of Méhul's composition through Sir Thomas's languid rendering of the camp awakening for a day of hunting, followed by a chase that is ratcheted up through an astonishing series of accelerations to final horn calls that are madness.
Around 1800, the popularity of such stormy dramas began to wane, replaced by a fashion for the lighter opéra comiques of composers such as Boieldieu. In addition, Mehul's friend Napoleon told him he preferred a more comic, less serious style of opera. As a Corsican, Napoleon's cultural background was Italian, and he loved the opera buffa of composers like Paisiello and Cimarosa. Méhul responded with L'Irato ("The Angry Man"), a one-act comedy premiered as the work of the Italian composer "Fiorelli" in 1801. When it became an immediate success, Méhul revealed the hoax he had played. Méhul also continued to compose works in a more serious vein. Joseph, based on the Biblical story of Joseph and his brothers, is the most famous of these later operas, but its success in France was short-lived. In Germany, however, it won many admirers throughout the nineteenth century, including Wagner.
Besides operas, Méhul composed a number of songs for the festivals of the republic (often commissioned by the emperor Napoleon), cantatas, and five symphonies in the years 1797 and 1808 to 1810.The First Symphony was revived in one of Felix Mendelssohn's concerts with the Leipzig Gewandhaus Orchestra in 1838 and 1846 to an audience including Robert Schumann, who was impressed by the piece. In all four movements there are some stylistic similarities with Beethoven's Symphony No.5 (including the dissonant, furious mood of the first movement and the string pizzicatos in the third), which were also noted by Schumann. Actually at this date only Beethoven's Symphonies No.1 and 2 (1799/1800 and 1802) had been performed in France and both Beethoven's Fifth and Mehul's First were composed in the same year, 1808, were published in the following, 1809. In his mature symphonies, Mehul continued the path Haydn (the Paris Symphonies, 1785-86, for example), Mozart (Symphony No. 40, K.550, 1788) had taken, two composers who enjoyed great popularity in France in the early 19th century. A fifth symphony was never completed - "as disillusionment and tuberculosis took their toll", as David Charlton pointed out. The Symphonoes nos.3 and 4 were only rediscovered by Charlton in 1979.