Born in Avignon, Vernet went to Rome at the age of twenty to become a history painter. He soon took to landscape painting after discovering the art of Claude Gellée, Salvator Rosa and Andrea Locatelli, and decided to join the studio of Adrien Manglard, a successful French marine painter. He travelled to Naples in 1737 and on many other occasions. By 1740, Vernet had established a reputation as a painter of marines, and French diplomats as well as English Grand tourists were to be among Vernet's most consistent patrons, the latter no doubt encouraged by Vernet's English wife, Virginia Cecilia Parker, the daughter of a captain in the papal navy, whom he married in 1745.
Official recognition in his own country began when he was approved by the Académie Royale in Paris in 1746, which enabled him to exhibit at the Salon that year for the first time. When Abel-François Poisson de Vandières, later marquis de Marigny and Directeur des Bâtiments, made his educational tour of Italy in 1750, he and his party visited Vernet's studio in Rome. It was on the marquis' initiative that, in 1753, Vernet was summoned back to France to paint the Ports de France, one of the most important royal commissions of Louis XV's reign. He continued working on this commission until 1765.