(b. ca. 1584, Pontoise, d. 1654, Paris)
French architect. He worked in Rome between 1607 and 1614, and studied the work of Giacomo della Porta. On his return to France, after several years working as an engineer building bridges, his first major commission was to complete the Parisian Church of the Oratorians (1616). Commissioned by Louis XIII, he built the Pavillon de l'Horloge at the Louvre (after 1624). After a large number of hotels and churches, he designed the palace and setting for the model city of Richelieu, for Cardinal Richelieu (begun 1631) and built the Palais Cardinal in Paris (now the Palais Royal, begun 1633).
A milestone in the development of classical Baroque in France can be seen as resulting from another commission from Richelieu, that of the church of the Sorbonne (begun 1626). Lemercier continued the work of Mansart (begun 1645) to construct the church of Val-de-Grace.
Together with Louis Le Vau and François Mansart, Lemercier formed the classicising French Baroque manner, drawing from French traditions of the previous century and current Roman practice, the fresh, essentially French synthesis associated with Cardinal Richelieu and Louis XIII.