He was born in Paris. His father had been intendant successively to the duc de Penthièvre, the comte de Toulouse and the unfortunate princesse de Lamballe, who was the boy's godmother. Lemercier was a prodigy; before he was sixteen his tragedy of Méléagre was produced at the Théâtre Français. Clarisse Harlowe (1792) provoked the criticism that the author was "pas assez roué pour peindre les roueries" (not enough scamp to depict scamp tricks.) Le Tartufe révolutionnaire a parody full of bold political allusions, was suppressed after the fifth performance.
In 1795 Lemercier's masterpiece Agamemnon, called by Charles Lafitte the last great antique tragedy in French literature, was produced. It was a great success, but was violently attacked later by Julien Louis Geoffroy who stigmatized it as a bad caricature of Prosper Jolyot de Crébillon. Les quatre métamorphoses (1799) was written to prove that the most indecent subjects might be treated without offence. The Pinto (1800) was the result of a wager that no further dramatic innovations were possible after the comedies of Pierre Beaumarchais. It is a historical comedy on the subject of the Portuguese Revolution of 1640. This play was construed as casting reflections on the first consul Napoleon, who had hitherto been a firm friend of Lemercier. His extreme freedom of speech finally offended Napoleon, and the quarrel proved disastrous to Lemercier's fortune for the time.
None of his subsequent work fulfilled the expectations raised by Agamemnon, with the exception perhaps of Frédégonde et Brunehaut (1821). In 1810 he was elected to the Académie française, where he consistently opposed the romanticists, refusing to vote for Victor Hugo - who was to succeed him. In spite of this, he has some pretensions to be considered the earliest of the romantic school. His Christophe Colomb (1809), advertised on the play-bill as a comédie shakespérienne (sic), represented the interior of a ship, and showed no respect for the classical unities. Its numerous innovations provoked such violent disturbances in the audience that one person was killed and future representations had to be guarded by the police.
Lemercier wrote four long and ambitious epic poems: Homère, Alexandre (1801), L'Atlantiade ou la théogonie newtonienne (1812) and Moïse (1823), as well as an extraordinary Panhypocrisiade (1819–1832), a distinctly romantic production in sixteen cantos, which has the sub-title Spectacle infernal du XVIe siècle. In it 16th century history, with Charles V and Francis I as principal personages, is played out on an imaginary stage by demons in the intervals of their sufferings. Lemercier died in Paris.