Gossec's own first symphony was performed in 1754, and as conductor to the Prince de Condé’s orchestra he produced several operas and other compositions of his own. He imposed his influence on French music with remarkable success. He premiered his Requiem in 1760, a piece ninety minutes in length, which made him famous overnight. The piece was later admired by Wolfgang Amadeus Mozart, who visited Gossec during a rather unsuccessful trip to Paris in 1778, and described him in a letter to his father as "a very good friend and a very dry man".
Gossec founded the Concert des Amateurs in 1770 and in 1773 he reorganised the Concert Spirituel together with Simon Leduc and Pierre Gaviniès. In this concert series he presented and conducted his own symphonies as well as those by his contemporaries, especially works by Joseph Haydn, whose music became more and more popular in Paris, and finally even superseded Gossec's symphonic work. In the 1780s, Gossec's symphonic output decreased and he concentrated on operas. He organized the École de Chant in 1784, together with Etienne Méhul, was conductor of the band of the Garde Nationale at the French Revolution, and was appointed (again with Méhul and Luigi Cherubini) inspector of the Conservatoire de Musique on its creation in 1795. He was an original member of the Institut and a chevalier of the Legion of Honour. In 1815, after the defeat of Napoleon at Waterloo, the Conservatoire was closed for some time by Louis XVIII, and the eighty-one year-old Gossec had to retire. Until 1817 he worked on his last composition, a third Te Deum, and was supported by a pension granted by the Conservatoire.
He died in the Parisian suburb of Passy. The funeral service was attended by former colleagues, including Cherubini, at the Père Lachaise cemetery in Paris. His grave is near those of Méhul and Grétry.
Some of his techniques seem to have anticipated the innovations of the Romantic era: he wrote a Te Deum for 1200 singers and 300 wind instruments; several oratorios include instructions for physical separation of multiple choirs, including invisible ones behind the stage. He wrote several works in honor of the French revolution, including Le Triomphe de la République, and L'Offrande à la Liberté.
Although most people would have difficulty recognizing Gossec's Gavotte by its title, the melody itself remains familiar in the United States and elsewhere because Carl Stalling used an arrangement of it in several Warner Brothers cartoons.
He was little known outside France, and his own numerous compositions, sacred and secular, were overshadowed by those of more famous composers; but he was an inspiration to many, and powerfully stimulated the revival of instrumental music.